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use crate::cmp::Ordering; use crate::ops::Try; use super::super::LoopState; use super::super::{Chain, Cycle, Copied, Cloned, Enumerate, Filter, FilterMap, Fuse}; use super::super::{Flatten, FlatMap}; use super::super::{Inspect, Map, Peekable, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile, Rev}; use super::super::{Zip, Sum, Product, FromIterator}; fn _assert_is_object_safe(_: &dyn Iterator<Item=()>) {} /// An interface for dealing with iterators. /// /// This is the main iterator trait. For more about the concept of iterators /// generally, please see the [module-level documentation]. In particular, you /// may want to know how to [implement `Iterator`][impl]. /// /// [module-level documentation]: index.html /// [impl]: index.html#implementing-iterator #[stable(feature = "rust1", since = "1.0.0")] #[rustc_on_unimplemented( on( _Self="[std::ops::Range<Idx>; 1]", label="if you meant to iterate between two values, remove the square brackets", note="`[start..end]` is an array of one `Range`; you might have meant to have a `Range` \ without the brackets: `start..end`" ), on( _Self="[std::ops::RangeFrom<Idx>; 1]", label="if you meant to iterate from a value onwards, remove the square brackets", note="`[start..]` is an array of one `RangeFrom`; you might have meant to have a \ `RangeFrom` without the brackets: `start..`, keeping in mind that iterating over an \ unbounded iterator will run forever unless you `break` or `return` from within the \ loop" ), on( _Self="[std::ops::RangeTo<Idx>; 1]", label="if you meant to iterate until a value, remove the square brackets and add a \ starting value", note="`[..end]` is an array of one `RangeTo`; you might have meant to have a bounded \ `Range` without the brackets: `0..end`" ), on( _Self="[std::ops::RangeInclusive<Idx>; 1]", label="if you meant to iterate between two values, remove the square brackets", note="`[start..=end]` is an array of one `RangeInclusive`; you might have meant to have a \ `RangeInclusive` without the brackets: `start..=end`" ), on( _Self="[std::ops::RangeToInclusive<Idx>; 1]", label="if you meant to iterate until a value (including it), remove the square brackets \ and add a starting value", note="`[..=end]` is an array of one `RangeToInclusive`; you might have meant to have a \ bounded `RangeInclusive` without the brackets: `0..=end`" ), on( _Self="std::ops::RangeTo<Idx>", label="if you meant to iterate until a value, add a starting value", note="`..end` is a `RangeTo`, which cannot be iterated on; you might have meant to have a \ bounded `Range`: `0..end`" ), on( _Self="std::ops::RangeToInclusive<Idx>", label="if you meant to iterate until a value (including it), add a starting value", note="`..=end` is a `RangeToInclusive`, which cannot be iterated on; you might have meant \ to have a bounded `RangeInclusive`: `0..=end`" ), on( _Self="&str", label="`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" ), on( _Self="std::string::String", label="`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" ), on( _Self="[]", label="borrow the array with `&` or call `.iter()` on it to iterate over it", note="arrays are not iterators, but slices like the following are: `&[1, 2, 3]`" ), on( _Self="{integral}", note="if you want to iterate between `start` until a value `end`, use the exclusive range \ syntax `start..end` or the inclusive range syntax `start..=end`" ), label="`{Self}` is not an iterator", message="`{Self}` is not an iterator" )] #[doc(spotlight)] #[must_use = "iterators are lazy and do nothing unless consumed"] pub trait Iterator { /// The type of the elements being iterated over. #[stable(feature = "rust1", since = "1.0.0")] type Item; /// Advances the iterator and returns the next value. /// /// Returns [`None`] when iteration is finished. Individual iterator /// implementations may choose to resume iteration, and so calling `next()` /// again may or may not eventually start returning [`Some(Item)`] again at some /// point. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// [`Some(Item)`]: ../../std/option/enum.Option.html#variant.Some /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// // A call to next() returns the next value... /// assert_eq!(Some(&1), iter.next()); /// assert_eq!(Some(&2), iter.next()); /// assert_eq!(Some(&3), iter.next()); /// /// // ... and then None once it's over. /// assert_eq!(None, iter.next()); /// /// // More calls may or may not return `None`. Here, they always will. /// assert_eq!(None, iter.next()); /// assert_eq!(None, iter.next()); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn next(&mut self) -> Option<Self::Item>; /// Returns the bounds on the remaining length of the iterator. /// /// Specifically, `size_hint()` returns a tuple where the first element /// is the lower bound, and the second element is the upper bound. /// /// The second half of the tuple that is returned is an [`Option`]`<`[`usize`]`>`. /// A [`None`] here means that either there is no known upper bound, or the /// upper bound is larger than [`usize`]. /// /// # Implementation notes /// /// It is not enforced that an iterator implementation yields the declared /// number of elements. A buggy iterator may yield less than the lower bound /// or more than the upper bound of elements. /// /// `size_hint()` is primarily intended to be used for optimizations such as /// reserving space for the elements of the iterator, but must not be /// trusted to e.g., omit bounds checks in unsafe code. An incorrect /// implementation of `size_hint()` should not lead to memory safety /// violations. /// /// That said, the implementation should provide a correct estimation, /// because otherwise it would be a violation of the trait's protocol. /// /// The default implementation returns `(0, `[`None`]`)` which is correct for any /// iterator. /// /// [`usize`]: ../../std/primitive.usize.html /// [`Option`]: ../../std/option/enum.Option.html /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// let iter = a.iter(); /// /// assert_eq!((3, Some(3)), iter.size_hint()); /// ``` /// /// A more complex example: /// /// ``` /// // The even numbers from zero to ten. /// let iter = (0..10).filter(|x| x % 2 == 0); /// /// // We might iterate from zero to ten times. Knowing that it's five /// // exactly wouldn't be possible without executing filter(). /// assert_eq!((0, Some(10)), iter.size_hint()); /// /// // Let's add five more numbers with chain() /// let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20); /// /// // now both bounds are increased by five /// assert_eq!((5, Some(15)), iter.size_hint()); /// ``` /// /// Returning `None` for an upper bound: /// /// ``` /// // an infinite iterator has no upper bound /// // and the maximum possible lower bound /// let iter = 0..; /// /// assert_eq!((usize::max_value(), None), iter.size_hint()); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn size_hint(&self) -> (usize, Option<usize>) { (0, None) } /// Consumes the iterator, counting the number of iterations and returning it. /// /// This method will evaluate the iterator until its [`next`] returns /// [`None`]. Once [`None`] is encountered, `count()` returns the number of /// times it called [`next`]. /// /// [`next`]: #tymethod.next /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Overflow Behavior /// /// The method does no guarding against overflows, so counting elements of /// an iterator with more than [`usize::MAX`] elements either produces the /// wrong result or panics. If debug assertions are enabled, a panic is /// guaranteed. /// /// # Panics /// /// This function might panic if the iterator has more than [`usize::MAX`] /// elements. /// /// [`usize::MAX`]: ../../std/usize/constant.MAX.html /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// assert_eq!(a.iter().count(), 3); /// /// let a = [1, 2, 3, 4, 5]; /// assert_eq!(a.iter().count(), 5); /// ``` #[inline] #[rustc_inherit_overflow_checks] #[stable(feature = "rust1", since = "1.0.0")] fn count(self) -> usize where Self: Sized { // Might overflow. self.fold(0, |cnt, _| cnt + 1) } /// Consumes the iterator, returning the last element. /// /// This method will evaluate the iterator until it returns [`None`]. While /// doing so, it keeps track of the current element. After [`None`] is /// returned, `last()` will then return the last element it saw. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// assert_eq!(a.iter().last(), Some(&3)); /// /// let a = [1, 2, 3, 4, 5]; /// assert_eq!(a.iter().last(), Some(&5)); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn last(self) -> Option<Self::Item> where Self: Sized { let mut last = None; for x in self { last = Some(x); } last } /// Returns the `n`th element of the iterator. /// /// Like most indexing operations, the count starts from zero, so `nth(0)` /// returns the first value, `nth(1)` the second, and so on. /// /// Note that all preceding elements, as well as the returned element, will be /// consumed from the iterator. That means that the preceding elements will be /// discarded, and also that calling `nth(0)` multiple times on the same iterator /// will return different elements. /// /// `nth()` will return [`None`] if `n` is greater than or equal to the length of the /// iterator. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// assert_eq!(a.iter().nth(1), Some(&2)); /// ``` /// /// Calling `nth()` multiple times doesn't rewind the iterator: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert_eq!(iter.nth(1), Some(&2)); /// assert_eq!(iter.nth(1), None); /// ``` /// /// Returning `None` if there are less than `n + 1` elements: /// /// ``` /// let a = [1, 2, 3]; /// assert_eq!(a.iter().nth(10), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn nth(&mut self, mut n: usize) -> Option<Self::Item> { for x in self { if n == 0 { return Some(x) } n -= 1; } None } /// Creates an iterator starting at the same point, but stepping by /// the given amount at each iteration. /// /// Note 1: The first element of the iterator will always be returned, /// regardless of the step given. /// /// Note 2: The time at which ignored elements are pulled is not fixed. /// `StepBy` behaves like the sequence `next(), nth(step-1), nth(step-1), …`, /// but is also free to behave like the sequence /// `advance_n_and_return_first(step), advance_n_and_return_first(step), …` /// Which way is used may change for some iterators for performance reasons. /// The second way will advance the iterator earlier and may consume more items. /// /// `advance_n_and_return_first` is the equivalent of: /// ``` /// fn advance_n_and_return_first<I>(iter: &mut I, total_step: usize) -> Option<I::Item> /// where /// I: Iterator, /// { /// let next = iter.next(); /// if total_step > 1 { /// iter.nth(total_step-2); /// } /// next /// } /// ``` /// /// # Panics /// /// The method will panic if the given step is `0`. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [0, 1, 2, 3, 4, 5]; /// let mut iter = a.iter().step_by(2); /// /// assert_eq!(iter.next(), Some(&0)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), Some(&4)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "iterator_step_by", since = "1.28.0")] fn step_by(self, step: usize) -> StepBy<Self> where Self: Sized { StepBy::new(self, step) } /// Takes two iterators and creates a new iterator over both in sequence. /// /// `chain()` will return a new iterator which will first iterate over /// values from the first iterator and then over values from the second /// iterator. /// /// In other words, it links two iterators together, in a chain. 🔗 /// /// # Examples /// /// Basic usage: /// /// ``` /// let a1 = [1, 2, 3]; /// let a2 = [4, 5, 6]; /// /// let mut iter = a1.iter().chain(a2.iter()); /// /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.next(), Some(&4)); /// assert_eq!(iter.next(), Some(&5)); /// assert_eq!(iter.next(), Some(&6)); /// assert_eq!(iter.next(), None); /// ``` /// /// Since the argument to `chain()` uses [`IntoIterator`], we can pass /// anything that can be converted into an [`Iterator`], not just an /// [`Iterator`] itself. For example, slices (`&[T]`) implement /// [`IntoIterator`], and so can be passed to `chain()` directly: /// /// [`IntoIterator`]: trait.IntoIterator.html /// [`Iterator`]: trait.Iterator.html /// /// ``` /// let s1 = &[1, 2, 3]; /// let s2 = &[4, 5, 6]; /// /// let mut iter = s1.iter().chain(s2); /// /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.next(), Some(&4)); /// assert_eq!(iter.next(), Some(&5)); /// assert_eq!(iter.next(), Some(&6)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where Self: Sized, U: IntoIterator<Item=Self::Item>, { Chain::new(self, other.into_iter()) } /// 'Zips up' two iterators into a single iterator of pairs. /// /// `zip()` returns a new iterator that will iterate over two other /// iterators, returning a tuple where the first element comes from the /// first iterator, and the second element comes from the second iterator. /// /// In other words, it zips two iterators together, into a single one. /// /// If either iterator returns [`None`], [`next`] from the zipped iterator /// will return [`None`]. If the first iterator returns [`None`], `zip` will /// short-circuit and `next` will not be called on the second iterator. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a1 = [1, 2, 3]; /// let a2 = [4, 5, 6]; /// /// let mut iter = a1.iter().zip(a2.iter()); /// /// assert_eq!(iter.next(), Some((&1, &4))); /// assert_eq!(iter.next(), Some((&2, &5))); /// assert_eq!(iter.next(), Some((&3, &6))); /// assert_eq!(iter.next(), None); /// ``` /// /// Since the argument to `zip()` uses [`IntoIterator`], we can pass /// anything that can be converted into an [`Iterator`], not just an /// [`Iterator`] itself. For example, slices (`&[T]`) implement /// [`IntoIterator`], and so can be passed to `zip()` directly: /// /// [`IntoIterator`]: trait.IntoIterator.html /// [`Iterator`]: trait.Iterator.html /// /// ``` /// let s1 = &[1, 2, 3]; /// let s2 = &[4, 5, 6]; /// /// let mut iter = s1.iter().zip(s2); /// /// assert_eq!(iter.next(), Some((&1, &4))); /// assert_eq!(iter.next(), Some((&2, &5))); /// assert_eq!(iter.next(), Some((&3, &6))); /// assert_eq!(iter.next(), None); /// ``` /// /// `zip()` is often used to zip an infinite iterator to a finite one. /// This works because the finite iterator will eventually return [`None`], /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate`]: /// /// ``` /// let enumerate: Vec<_> = "foo".chars().enumerate().collect(); /// /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect(); /// /// assert_eq!((0, 'f'), enumerate[0]); /// assert_eq!((0, 'f'), zipper[0]); /// /// assert_eq!((1, 'o'), enumerate[1]); /// assert_eq!((1, 'o'), zipper[1]); /// /// assert_eq!((2, 'o'), enumerate[2]); /// assert_eq!((2, 'o'), zipper[2]); /// ``` /// /// [`enumerate`]: trait.Iterator.html#method.enumerate /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next /// [`None`]: ../../std/option/enum.Option.html#variant.None #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where Self: Sized, U: IntoIterator { Zip::new(self, other.into_iter()) } /// Takes a closure and creates an iterator which calls that closure on each /// element. /// /// `map()` transforms one iterator into another, by means of its argument: /// something that implements [`FnMut`]. It produces a new iterator which /// calls this closure on each element of the original iterator. /// /// If you are good at thinking in types, you can think of `map()` like this: /// If you have an iterator that gives you elements of some type `A`, and /// you want an iterator of some other type `B`, you can use `map()`, /// passing a closure that takes an `A` and returns a `B`. /// /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is /// lazy, it is best used when you're already working with other iterators. /// If you're doing some sort of looping for a side effect, it's considered /// more idiomatic to use [`for`] than `map()`. /// /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for /// [`FnMut`]: ../../std/ops/trait.FnMut.html /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().map(|x| 2 * x); /// /// assert_eq!(iter.next(), Some(2)); /// assert_eq!(iter.next(), Some(4)); /// assert_eq!(iter.next(), Some(6)); /// assert_eq!(iter.next(), None); /// ``` /// /// If you're doing some sort of side effect, prefer [`for`] to `map()`: /// /// ``` /// # #![allow(unused_must_use)] /// // don't do this: /// (0..5).map(|x| println!("{}", x)); /// /// // it won't even execute, as it is lazy. Rust will warn you about this. /// /// // Instead, use for: /// for x in 0..5 { /// println!("{}", x); /// } /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn map<B, F>(self, f: F) -> Map<Self, F> where Self: Sized, F: FnMut(Self::Item) -> B, { Map::new(self, f) } /// Calls a closure on each element of an iterator. /// /// This is equivalent to using a [`for`] loop on the iterator, although /// `break` and `continue` are not possible from a closure. It's generally /// more idiomatic to use a `for` loop, but `for_each` may be more legible /// when processing items at the end of longer iterator chains. In some /// cases `for_each` may also be faster than a loop, because it will use /// internal iteration on adaptors like `Chain`. /// /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for /// /// # Examples /// /// Basic usage: /// /// ``` /// use std::sync::mpsc::channel; /// /// let (tx, rx) = channel(); /// (0..5).map(|x| x * 2 + 1) /// .for_each(move |x| tx.send(x).unwrap()); /// /// let v: Vec<_> = rx.iter().collect(); /// assert_eq!(v, vec![1, 3, 5, 7, 9]); /// ``` /// /// For such a small example, a `for` loop may be cleaner, but `for_each` /// might be preferable to keep a functional style with longer iterators: /// /// ``` /// (0..5).flat_map(|x| x * 100 .. x * 110) /// .enumerate() /// .filter(|&(i, x)| (i + x) % 3 == 0) /// .for_each(|(i, x)| println!("{}:{}", i, x)); /// ``` #[inline] #[stable(feature = "iterator_for_each", since = "1.21.0")] fn for_each<F>(self, mut f: F) where Self: Sized, F: FnMut(Self::Item), { self.fold((), move |(), item| f(item)); } /// Creates an iterator which uses a closure to determine if an element /// should be yielded. /// /// The closure must return `true` or `false`. `filter()` creates an /// iterator which calls this closure on each element. If the closure /// returns `true`, then the element is returned. If the closure returns /// `false`, it will try again, and call the closure on the next element, /// seeing if it passes the test. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [0i32, 1, 2]; /// /// let mut iter = a.iter().filter(|x| x.is_positive()); /// /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// Because the closure passed to `filter()` takes a reference, and many /// iterators iterate over references, this leads to a possibly confusing /// situation, where the type of the closure is a double reference: /// /// ``` /// let a = [0, 1, 2]; /// /// let mut iter = a.iter().filter(|x| **x > 1); // need two *s! /// /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// It's common to instead use destructuring on the argument to strip away /// one: /// /// ``` /// let a = [0, 1, 2]; /// /// let mut iter = a.iter().filter(|&x| *x > 1); // both & and * /// /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// or both: /// /// ``` /// let a = [0, 1, 2]; /// /// let mut iter = a.iter().filter(|&&x| x > 1); // two &s /// /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// of these layers. #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn filter<P>(self, predicate: P) -> Filter<Self, P> where Self: Sized, P: FnMut(&Self::Item) -> bool, { Filter::new(self, predicate) } /// Creates an iterator that both filters and maps. /// /// The closure must return an [`Option<T>`]. `filter_map` creates an /// iterator which calls this closure on each element. If the closure /// returns [`Some(element)`][`Some`], then that element is returned. If the /// closure returns [`None`], it will try again, and call the closure on the /// next element, seeing if it will return [`Some`]. /// /// Why `filter_map` and not just [`filter`] and [`map`]? The key is in this /// part: /// /// [`filter`]: #method.filter /// [`map`]: #method.map /// /// > If the closure returns [`Some(element)`][`Some`], then that element is returned. /// /// In other words, it removes the [`Option<T>`] layer automatically. If your /// mapping is already returning an [`Option<T>`] and you want to skip over /// [`None`]s, then `filter_map` is much, much nicer to use. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = ["1", "lol", "3", "NaN", "5"]; /// /// let mut iter = a.iter().filter_map(|s| s.parse().ok()); /// /// assert_eq!(iter.next(), Some(1)); /// assert_eq!(iter.next(), Some(3)); /// assert_eq!(iter.next(), Some(5)); /// assert_eq!(iter.next(), None); /// ``` /// /// Here's the same example, but with [`filter`] and [`map`]: /// /// ``` /// let a = ["1", "lol", "3", "NaN", "5"]; /// let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap()); /// assert_eq!(iter.next(), Some(1)); /// assert_eq!(iter.next(), Some(3)); /// assert_eq!(iter.next(), Some(5)); /// assert_eq!(iter.next(), None); /// ``` /// /// [`Option<T>`]: ../../std/option/enum.Option.html /// [`Some`]: ../../std/option/enum.Option.html#variant.Some /// [`None`]: ../../std/option/enum.Option.html#variant.None #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where Self: Sized, F: FnMut(Self::Item) -> Option<B>, { FilterMap::new(self, f) } /// Creates an iterator which gives the current iteration count as well as /// the next value. /// /// The iterator returned yields pairs `(i, val)`, where `i` is the /// current index of iteration and `val` is the value returned by the /// iterator. /// /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a /// different sized integer, the [`zip`] function provides similar /// functionality. /// /// # Overflow Behavior /// /// The method does no guarding against overflows, so enumerating more than /// [`usize::MAX`] elements either produces the wrong result or panics. If /// debug assertions are enabled, a panic is guaranteed. /// /// # Panics /// /// The returned iterator might panic if the to-be-returned index would /// overflow a [`usize`]. /// /// [`usize::MAX`]: ../../std/usize/constant.MAX.html /// [`usize`]: ../../std/primitive.usize.html /// [`zip`]: #method.zip /// /// # Examples /// /// ``` /// let a = ['a', 'b', 'c']; /// /// let mut iter = a.iter().enumerate(); /// /// assert_eq!(iter.next(), Some((0, &'a'))); /// assert_eq!(iter.next(), Some((1, &'b'))); /// assert_eq!(iter.next(), Some((2, &'c'))); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn enumerate(self) -> Enumerate<Self> where Self: Sized { Enumerate::new(self) } /// Creates an iterator which can use `peek` to look at the next element of /// the iterator without consuming it. /// /// Adds a [`peek`] method to an iterator. See its documentation for /// more information. /// /// Note that the underlying iterator is still advanced when [`peek`] is /// called for the first time: In order to retrieve the next element, /// [`next`] is called on the underlying iterator, hence any side effects (i.e. /// anything other than fetching the next value) of the [`next`] method /// will occur. /// /// [`peek`]: struct.Peekable.html#method.peek /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next /// /// # Examples /// /// Basic usage: /// /// ``` /// let xs = [1, 2, 3]; /// /// let mut iter = xs.iter().peekable(); /// /// // peek() lets us see into the future /// assert_eq!(iter.peek(), Some(&&1)); /// assert_eq!(iter.next(), Some(&1)); /// /// assert_eq!(iter.next(), Some(&2)); /// /// // we can peek() multiple times, the iterator won't advance /// assert_eq!(iter.peek(), Some(&&3)); /// assert_eq!(iter.peek(), Some(&&3)); /// /// assert_eq!(iter.next(), Some(&3)); /// /// // after the iterator is finished, so is peek() /// assert_eq!(iter.peek(), None); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn peekable(self) -> Peekable<Self> where Self: Sized { Peekable::new(self) } /// Creates an iterator that [`skip`]s elements based on a predicate. /// /// [`skip`]: #method.skip /// /// `skip_while()` takes a closure as an argument. It will call this /// closure on each element of the iterator, and ignore elements /// until it returns `false`. /// /// After `false` is returned, `skip_while()`'s job is over, and the /// rest of the elements are yielded. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [-1i32, 0, 1]; /// /// let mut iter = a.iter().skip_while(|x| x.is_negative()); /// /// assert_eq!(iter.next(), Some(&0)); /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), None); /// ``` /// /// Because the closure passed to `skip_while()` takes a reference, and many /// iterators iterate over references, this leads to a possibly confusing /// situation, where the type of the closure is a double reference: /// /// ``` /// let a = [-1, 0, 1]; /// /// let mut iter = a.iter().skip_while(|x| **x < 0); // need two *s! /// /// assert_eq!(iter.next(), Some(&0)); /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), None); /// ``` /// /// Stopping after an initial `false`: /// /// ``` /// let a = [-1, 0, 1, -2]; /// /// let mut iter = a.iter().skip_while(|x| **x < 0); /// /// assert_eq!(iter.next(), Some(&0)); /// assert_eq!(iter.next(), Some(&1)); /// /// // while this would have been false, since we already got a false, /// // skip_while() isn't used any more /// assert_eq!(iter.next(), Some(&-2)); /// /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where Self: Sized, P: FnMut(&Self::Item) -> bool, { SkipWhile::new(self, predicate) } /// Creates an iterator that yields elements based on a predicate. /// /// `take_while()` takes a closure as an argument. It will call this /// closure on each element of the iterator, and yield elements /// while it returns `true`. /// /// After `false` is returned, `take_while()`'s job is over, and the /// rest of the elements are ignored. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [-1i32, 0, 1]; /// /// let mut iter = a.iter().take_while(|x| x.is_negative()); /// /// assert_eq!(iter.next(), Some(&-1)); /// assert_eq!(iter.next(), None); /// ``` /// /// Because the closure passed to `take_while()` takes a reference, and many /// iterators iterate over references, this leads to a possibly confusing /// situation, where the type of the closure is a double reference: /// /// ``` /// let a = [-1, 0, 1]; /// /// let mut iter = a.iter().take_while(|x| **x < 0); // need two *s! /// /// assert_eq!(iter.next(), Some(&-1)); /// assert_eq!(iter.next(), None); /// ``` /// /// Stopping after an initial `false`: /// /// ``` /// let a = [-1, 0, 1, -2]; /// /// let mut iter = a.iter().take_while(|x| **x < 0); /// /// assert_eq!(iter.next(), Some(&-1)); /// /// // We have more elements that are less than zero, but since we already /// // got a false, take_while() isn't used any more /// assert_eq!(iter.next(), None); /// ``` /// /// Because `take_while()` needs to look at the value in order to see if it /// should be included or not, consuming iterators will see that it is /// removed: /// /// ``` /// let a = [1, 2, 3, 4]; /// let mut iter = a.iter(); /// /// let result: Vec<i32> = iter.by_ref() /// .take_while(|n| **n != 3) /// .cloned() /// .collect(); /// /// assert_eq!(result, &[1, 2]); /// /// let result: Vec<i32> = iter.cloned().collect(); /// /// assert_eq!(result, &[4]); /// ``` /// /// The `3` is no longer there, because it was consumed in order to see if /// the iteration should stop, but wasn't placed back into the iterator. #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where Self: Sized, P: FnMut(&Self::Item) -> bool, { TakeWhile::new(self, predicate) } /// Creates an iterator that skips the first `n` elements. /// /// After they have been consumed, the rest of the elements are yielded. /// Rather than overriding this method directly, instead override the `nth` method. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().skip(2); /// /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn skip(self, n: usize) -> Skip<Self> where Self: Sized { Skip::new(self, n) } /// Creates an iterator that yields its first `n` elements. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().take(2); /// /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// `take()` is often used with an infinite iterator, to make it finite: /// /// ``` /// let mut iter = (0..).take(3); /// /// assert_eq!(iter.next(), Some(0)); /// assert_eq!(iter.next(), Some(1)); /// assert_eq!(iter.next(), Some(2)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn take(self, n: usize) -> Take<Self> where Self: Sized, { Take::new(self, n) } /// An iterator adaptor similar to [`fold`] that holds internal state and /// produces a new iterator. /// /// [`fold`]: #method.fold /// /// `scan()` takes two arguments: an initial value which seeds the internal /// state, and a closure with two arguments, the first being a mutable /// reference to the internal state and the second an iterator element. /// The closure can assign to the internal state to share state between /// iterations. /// /// On iteration, the closure will be applied to each element of the /// iterator and the return value from the closure, an [`Option`], is /// yielded by the iterator. /// /// [`Option`]: ../../std/option/enum.Option.html /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().scan(1, |state, &x| { /// // each iteration, we'll multiply the state by the element /// *state = *state * x; /// /// // then, we'll yield the negation of the state /// Some(-*state) /// }); /// /// assert_eq!(iter.next(), Some(-1)); /// assert_eq!(iter.next(), Some(-2)); /// assert_eq!(iter.next(), Some(-6)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>, { Scan::new(self, initial_state, f) } /// Creates an iterator that works like map, but flattens nested structure. /// /// The [`map`] adapter is very useful, but only when the closure /// argument produces values. If it produces an iterator instead, there's /// an extra layer of indirection. `flat_map()` will remove this extra layer /// on its own. /// /// You can think of `flat_map(f)` as the semantic equivalent /// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`. /// /// Another way of thinking about `flat_map()`: [`map`]'s closure returns /// one item for each element, and `flat_map()`'s closure returns an /// iterator for each element. /// /// [`map`]: #method.map /// [`flatten`]: #method.flatten /// /// # Examples /// /// Basic usage: /// /// ``` /// let words = ["alpha", "beta", "gamma"]; /// /// // chars() returns an iterator /// let merged: String = words.iter() /// .flat_map(|s| s.chars()) /// .collect(); /// assert_eq!(merged, "alphabetagamma"); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U, { FlatMap::new(self, f) } /// Creates an iterator that flattens nested structure. /// /// This is useful when you have an iterator of iterators or an iterator of /// things that can be turned into iterators and you want to remove one /// level of indirection. /// /// # Examples /// /// Basic usage: /// /// ``` /// let data = vec![vec![1, 2, 3, 4], vec![5, 6]]; /// let flattened = data.into_iter().flatten().collect::<Vec<u8>>(); /// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]); /// ``` /// /// Mapping and then flattening: /// /// ``` /// let words = ["alpha", "beta", "gamma"]; /// /// // chars() returns an iterator /// let merged: String = words.iter() /// .map(|s| s.chars()) /// .flatten() /// .collect(); /// assert_eq!(merged, "alphabetagamma"); /// ``` /// /// You can also rewrite this in terms of [`flat_map()`], which is preferable /// in this case since it conveys intent more clearly: /// /// ``` /// let words = ["alpha", "beta", "gamma"]; /// /// // chars() returns an iterator /// let merged: String = words.iter() /// .flat_map(|s| s.chars()) /// .collect(); /// assert_eq!(merged, "alphabetagamma"); /// ``` /// /// Flattening once only removes one level of nesting: /// /// ``` /// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]; /// /// let d2 = d3.iter().flatten().collect::<Vec<_>>(); /// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]); /// /// let d1 = d3.iter().flatten().flatten().collect::<Vec<_>>(); /// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]); /// ``` /// /// Here we see that `flatten()` does not perform a "deep" flatten. /// Instead, only one level of nesting is removed. That is, if you /// `flatten()` a three-dimensional array the result will be /// two-dimensional and not one-dimensional. To get a one-dimensional /// structure, you have to `flatten()` again. /// /// [`flat_map()`]: #method.flat_map #[inline] #[stable(feature = "iterator_flatten", since = "1.29.0")] fn flatten(self) -> Flatten<Self> where Self: Sized, Self::Item: IntoIterator { Flatten::new(self) } /// Creates an iterator which ends after the first [`None`]. /// /// After an iterator returns [`None`], future calls may or may not yield /// [`Some(T)`] again. `fuse()` adapts an iterator, ensuring that after a /// [`None`] is given, it will always return [`None`] forever. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// [`Some(T)`]: ../../std/option/enum.Option.html#variant.Some /// /// # Examples /// /// Basic usage: /// /// ``` /// // an iterator which alternates between Some and None /// struct Alternate { /// state: i32, /// } /// /// impl Iterator for Alternate { /// type Item = i32; /// /// fn next(&mut self) -> Option<i32> { /// let val = self.state; /// self.state = self.state + 1; /// /// // if it's even, Some(i32), else None /// if val % 2 == 0 { /// Some(val) /// } else { /// None /// } /// } /// } /// /// let mut iter = Alternate { state: 0 }; /// /// // we can see our iterator going back and forth /// assert_eq!(iter.next(), Some(0)); /// assert_eq!(iter.next(), None); /// assert_eq!(iter.next(), Some(2)); /// assert_eq!(iter.next(), None); /// /// // however, once we fuse it... /// let mut iter = iter.fuse(); /// /// assert_eq!(iter.next(), Some(4)); /// assert_eq!(iter.next(), None); /// /// // it will always return `None` after the first time. /// assert_eq!(iter.next(), None); /// assert_eq!(iter.next(), None); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn fuse(self) -> Fuse<Self> where Self: Sized { Fuse::new(self) } /// Do something with each element of an iterator, passing the value on. /// /// When using iterators, you'll often chain several of them together. /// While working on such code, you might want to check out what's /// happening at various parts in the pipeline. To do that, insert /// a call to `inspect()`. /// /// It's more common for `inspect()` to be used as a debugging tool than to /// exist in your final code, but applications may find it useful in certain /// situations when errors need to be logged before being discarded. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 4, 2, 3]; /// /// // this iterator sequence is complex. /// let sum = a.iter() /// .cloned() /// .filter(|x| x % 2 == 0) /// .fold(0, |sum, i| sum + i); /// /// println!("{}", sum); /// /// // let's add some inspect() calls to investigate what's happening /// let sum = a.iter() /// .cloned() /// .inspect(|x| println!("about to filter: {}", x)) /// .filter(|x| x % 2 == 0) /// .inspect(|x| println!("made it through filter: {}", x)) /// .fold(0, |sum, i| sum + i); /// /// println!("{}", sum); /// ``` /// /// This will print: /// /// ```text /// 6 /// about to filter: 1 /// about to filter: 4 /// made it through filter: 4 /// about to filter: 2 /// made it through filter: 2 /// about to filter: 3 /// 6 /// ``` /// /// Logging errors before discarding them: /// /// ``` /// let lines = ["1", "2", "a"]; /// /// let sum: i32 = lines /// .iter() /// .map(|line| line.parse::<i32>()) /// .inspect(|num| { /// if let Err(ref e) = *num { /// println!("Parsing error: {}", e); /// } /// }) /// .filter_map(Result::ok) /// .sum(); /// /// println!("Sum: {}", sum); /// ``` /// /// This will print: /// /// ```text /// Parsing error: invalid digit found in string /// Sum: 3 /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn inspect<F>(self, f: F) -> Inspect<Self, F> where Self: Sized, F: FnMut(&Self::Item), { Inspect::new(self, f) } /// Borrows an iterator, rather than consuming it. /// /// This is useful to allow applying iterator adaptors while still /// retaining ownership of the original iterator. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let iter = a.iter(); /// /// let sum: i32 = iter.take(5).fold(0, |acc, i| acc + i ); /// /// assert_eq!(sum, 6); /// /// // if we try to use iter again, it won't work. The following line /// // gives "error: use of moved value: `iter` /// // assert_eq!(iter.next(), None); /// /// // let's try that again /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// // instead, we add in a .by_ref() /// let sum: i32 = iter.by_ref().take(2).fold(0, |acc, i| acc + i ); /// /// assert_eq!(sum, 3); /// /// // now this is just fine: /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.next(), None); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn by_ref(&mut self) -> &mut Self where Self: Sized { self } /// Transforms an iterator into a collection. /// /// `collect()` can take anything iterable, and turn it into a relevant /// collection. This is one of the more powerful methods in the standard /// library, used in a variety of contexts. /// /// The most basic pattern in which `collect()` is used is to turn one /// collection into another. You take a collection, call [`iter`] on it, /// do a bunch of transformations, and then `collect()` at the end. /// /// One of the keys to `collect()`'s power is that many things you might /// not think of as 'collections' actually are. For example, a [`String`] /// is a collection of [`char`]s. And a collection of /// [`Result<T, E>`][`Result`] can be thought of as single /// [`Result`]`<Collection<T>, E>`. See the examples below for more. /// /// Because `collect()` is so general, it can cause problems with type /// inference. As such, `collect()` is one of the few times you'll see /// the syntax affectionately known as the 'turbofish': `::<>`. This /// helps the inference algorithm understand specifically which collection /// you're trying to collect into. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let doubled: Vec<i32> = a.iter() /// .map(|&x| x * 2) /// .collect(); /// /// assert_eq!(vec![2, 4, 6], doubled); /// ``` /// /// Note that we needed the `: Vec<i32>` on the left-hand side. This is because /// we could collect into, for example, a [`VecDeque<T>`] instead: /// /// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html /// /// ``` /// use std::collections::VecDeque; /// /// let a = [1, 2, 3]; /// /// let doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect(); /// /// assert_eq!(2, doubled[0]); /// assert_eq!(4, doubled[1]); /// assert_eq!(6, doubled[2]); /// ``` /// /// Using the 'turbofish' instead of annotating `doubled`: /// /// ``` /// let a = [1, 2, 3]; /// /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>(); /// /// assert_eq!(vec![2, 4, 6], doubled); /// ``` /// /// Because `collect()` only cares about what you're collecting into, you can /// still use a partial type hint, `_`, with the turbofish: /// /// ``` /// let a = [1, 2, 3]; /// /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>(); /// /// assert_eq!(vec![2, 4, 6], doubled); /// ``` /// /// Using `collect()` to make a [`String`]: /// /// ``` /// let chars = ['g', 'd', 'k', 'k', 'n']; /// /// let hello: String = chars.iter() /// .map(|&x| x as u8) /// .map(|x| (x + 1) as char) /// .collect(); /// /// assert_eq!("hello", hello); /// ``` /// /// If you have a list of [`Result<T, E>`][`Result`]s, you can use `collect()` to /// see if any of them failed: /// /// ``` /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")]; /// /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); /// /// // gives us the first error /// assert_eq!(Err("nope"), result); /// /// let results = [Ok(1), Ok(3)]; /// /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); /// /// // gives us the list of answers /// assert_eq!(Ok(vec![1, 3]), result); /// ``` /// /// [`iter`]: ../../std/iter/trait.Iterator.html#tymethod.next /// [`String`]: ../../std/string/struct.String.html /// [`char`]: ../../std/primitive.char.html /// [`Result`]: ../../std/result/enum.Result.html #[inline] #[stable(feature = "rust1", since = "1.0.0")] #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"] fn collect<B: FromIterator<Self::Item>>(self) -> B where Self: Sized { FromIterator::from_iter(self) } /// Consumes an iterator, creating two collections from it. /// /// The predicate passed to `partition()` can return `true`, or `false`. /// `partition()` returns a pair, all of the elements for which it returned /// `true`, and all of the elements for which it returned `false`. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let (even, odd): (Vec<i32>, Vec<i32>) = a /// .iter() /// .partition(|&n| n % 2 == 0); /// /// assert_eq!(even, vec![2]); /// assert_eq!(odd, vec![1, 3]); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn partition<B, F>(self, mut f: F) -> (B, B) where Self: Sized, B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool { let mut left: B = Default::default(); let mut right: B = Default::default(); for x in self { if f(&x) { left.extend(Some(x)) } else { right.extend(Some(x)) } } (left, right) } /// An iterator method that applies a function as long as it returns /// successfully, producing a single, final value. /// /// `try_fold()` takes two arguments: an initial value, and a closure with /// two arguments: an 'accumulator', and an element. The closure either /// returns successfully, with the value that the accumulator should have /// for the next iteration, or it returns failure, with an error value that /// is propagated back to the caller immediately (short-circuiting). /// /// The initial value is the value the accumulator will have on the first /// call. If applying the closure succeeded against every element of the /// iterator, `try_fold()` returns the final accumulator as success. /// /// Folding is useful whenever you have a collection of something, and want /// to produce a single value from it. /// /// # Note to Implementors /// /// Most of the other (forward) methods have default implementations in /// terms of this one, so try to implement this explicitly if it can /// do something better than the default `for` loop implementation. /// /// In particular, try to have this call `try_fold()` on the internal parts /// from which this iterator is composed. If multiple calls are needed, /// the `?` operator may be convenient for chaining the accumulator value /// along, but beware any invariants that need to be upheld before those /// early returns. This is a `&mut self` method, so iteration needs to be /// resumable after hitting an error here. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// // the checked sum of all of the elements of the array /// let sum = a.iter().try_fold(0i8, |acc, &x| acc.checked_add(x)); /// /// assert_eq!(sum, Some(6)); /// ``` /// /// Short-circuiting: /// /// ``` /// let a = [10, 20, 30, 100, 40, 50]; /// let mut it = a.iter(); /// /// // This sum overflows when adding the 100 element /// let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x)); /// assert_eq!(sum, None); /// /// // Because it short-circuited, the remaining elements are still /// // available through the iterator. /// assert_eq!(it.len(), 2); /// assert_eq!(it.next(), Some(&40)); /// ``` #[inline] #[stable(feature = "iterator_try_fold", since = "1.27.0")] fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B> { let mut accum = init; while let Some(x) = self.next() { accum = f(accum, x)?; } Try::from_ok(accum) } /// An iterator method that applies a fallible function to each item in the /// iterator, stopping at the first error and returning that error. /// /// This can also be thought of as the fallible form of [`for_each()`] /// or as the stateless version of [`try_fold()`]. /// /// [`for_each()`]: #method.for_each /// [`try_fold()`]: #method.try_fold /// /// # Examples /// /// ``` /// use std::fs::rename; /// use std::io::{stdout, Write}; /// use std::path::Path; /// /// let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"]; /// /// let res = data.iter().try_for_each(|x| writeln!(stdout(), "{}", x)); /// assert!(res.is_ok()); /// /// let mut it = data.iter().cloned(); /// let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old"))); /// assert!(res.is_err()); /// // It short-circuited, so the remaining items are still in the iterator: /// assert_eq!(it.next(), Some("stale_bread.json")); /// ``` #[inline] #[stable(feature = "iterator_try_fold", since = "1.27.0")] fn try_for_each<F, R>(&mut self, mut f: F) -> R where Self: Sized, F: FnMut(Self::Item) -> R, R: Try<Ok=()> { self.try_fold((), move |(), x| f(x)) } /// An iterator method that applies a function, producing a single, final value. /// /// `fold()` takes two arguments: an initial value, and a closure with two /// arguments: an 'accumulator', and an element. The closure returns the value that /// the accumulator should have for the next iteration. /// /// The initial value is the value the accumulator will have on the first /// call. /// /// After applying this closure to every element of the iterator, `fold()` /// returns the accumulator. /// /// This operation is sometimes called 'reduce' or 'inject'. /// /// Folding is useful whenever you have a collection of something, and want /// to produce a single value from it. /// /// Note: `fold()`, and similar methods that traverse the entire iterator, /// may not terminate for infinite iterators, even on traits for which a /// result is determinable in finite time. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// // the sum of all of the elements of the array /// let sum = a.iter().fold(0, |acc, x| acc + x); /// /// assert_eq!(sum, 6); /// ``` /// /// Let's walk through each step of the iteration here: /// /// | element | acc | x | result | /// |---------|-----|---|--------| /// | | 0 | | | /// | 1 | 0 | 1 | 1 | /// | 2 | 1 | 2 | 3 | /// | 3 | 3 | 3 | 6 | /// /// And so, our final result, `6`. /// /// It's common for people who haven't used iterators a lot to /// use a `for` loop with a list of things to build up a result. Those /// can be turned into `fold()`s: /// /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for /// /// ``` /// let numbers = [1, 2, 3, 4, 5]; /// /// let mut result = 0; /// /// // for loop: /// for i in &numbers { /// result = result + i; /// } /// /// // fold: /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x); /// /// // they're the same /// assert_eq!(result, result2); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn fold<B, F>(mut self, init: B, mut f: F) -> B where Self: Sized, F: FnMut(B, Self::Item) -> B, { self.try_fold(init, move |acc, x| Ok::<B, !>(f(acc, x))).unwrap() } /// Tests if every element of the iterator matches a predicate. /// /// `all()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, and if they all return /// `true`, then so does `all()`. If any of them return `false`, it /// returns `false`. /// /// `all()` is short-circuiting; in other words, it will stop processing /// as soon as it finds a `false`, given that no matter what else happens, /// the result will also be `false`. /// /// An empty iterator returns `true`. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert!(a.iter().all(|&x| x > 0)); /// /// assert!(!a.iter().all(|&x| x > 2)); /// ``` /// /// Stopping at the first `false`: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert!(!iter.all(|&x| x != 2)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&3)); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn all<F>(&mut self, mut f: F) -> bool where Self: Sized, F: FnMut(Self::Item) -> bool { self.try_for_each(move |x| { if f(x) { LoopState::Continue(()) } else { LoopState::Break(()) } }) == LoopState::Continue(()) } /// Tests if any element of the iterator matches a predicate. /// /// `any()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, and if any of them return /// `true`, then so does `any()`. If they all return `false`, it /// returns `false`. /// /// `any()` is short-circuiting; in other words, it will stop processing /// as soon as it finds a `true`, given that no matter what else happens, /// the result will also be `true`. /// /// An empty iterator returns `false`. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert!(a.iter().any(|&x| x > 0)); /// /// assert!(!a.iter().any(|&x| x > 5)); /// ``` /// /// Stopping at the first `true`: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert!(iter.any(|&x| x != 2)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&2)); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn any<F>(&mut self, mut f: F) -> bool where Self: Sized, F: FnMut(Self::Item) -> bool { self.try_for_each(move |x| { if f(x) { LoopState::Break(()) } else { LoopState::Continue(()) } }) == LoopState::Break(()) } /// Searches for an element of an iterator that satisfies a predicate. /// /// `find()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, and if any of them return /// `true`, then `find()` returns [`Some(element)`]. If they all return /// `false`, it returns [`None`]. /// /// `find()` is short-circuiting; in other words, it will stop processing /// as soon as the closure returns `true`. /// /// Because `find()` takes a reference, and many iterators iterate over /// references, this leads to a possibly confusing situation where the /// argument is a double reference. You can see this effect in the /// examples below, with `&&x`. /// /// [`Some(element)`]: ../../std/option/enum.Option.html#variant.Some /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2)); /// /// assert_eq!(a.iter().find(|&&x| x == 5), None); /// ``` /// /// Stopping at the first `true`: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert_eq!(iter.find(|&&x| x == 2), Some(&2)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&3)); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn find<P>(&mut self, mut predicate: P) -> Option<Self::Item> where Self: Sized, P: FnMut(&Self::Item) -> bool, { self.try_for_each(move |x| { if predicate(&x) { LoopState::Break(x) } else { LoopState::Continue(()) } }).break_value() } /// Applies function to the elements of iterator and returns /// the first non-none result. /// /// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`. /// /// /// # Examples /// /// ``` /// let a = ["lol", "NaN", "2", "5"]; /// /// let first_number = a.iter().find_map(|s| s.parse().ok()); /// /// assert_eq!(first_number, Some(2)); /// ``` #[inline] #[stable(feature = "iterator_find_map", since = "1.30.0")] fn find_map<B, F>(&mut self, mut f: F) -> Option<B> where Self: Sized, F: FnMut(Self::Item) -> Option<B>, { self.try_for_each(move |x| { match f(x) { Some(x) => LoopState::Break(x), None => LoopState::Continue(()), } }).break_value() } /// Searches for an element in an iterator, returning its index. /// /// `position()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, and if one of them /// returns `true`, then `position()` returns [`Some(index)`]. If all of /// them return `false`, it returns [`None`]. /// /// `position()` is short-circuiting; in other words, it will stop /// processing as soon as it finds a `true`. /// /// # Overflow Behavior /// /// The method does no guarding against overflows, so if there are more /// than [`usize::MAX`] non-matching elements, it either produces the wrong /// result or panics. If debug assertions are enabled, a panic is /// guaranteed. /// /// # Panics /// /// This function might panic if the iterator has more than `usize::MAX` /// non-matching elements. /// /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some /// [`None`]: ../../std/option/enum.Option.html#variant.None /// [`usize::MAX`]: ../../std/usize/constant.MAX.html /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert_eq!(a.iter().position(|&x| x == 2), Some(1)); /// /// assert_eq!(a.iter().position(|&x| x == 5), None); /// ``` /// /// Stopping at the first `true`: /// /// ``` /// let a = [1, 2, 3, 4]; /// /// let mut iter = a.iter(); /// /// assert_eq!(iter.position(|&x| x >= 2), Some(1)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&3)); /// /// // The returned index depends on iterator state /// assert_eq!(iter.position(|&x| x == 4), Some(0)); /// /// ``` #[inline] #[rustc_inherit_overflow_checks] #[stable(feature = "rust1", since = "1.0.0")] fn position<P>(&mut self, mut predicate: P) -> Option<usize> where Self: Sized, P: FnMut(Self::Item) -> bool, { // The addition might panic on overflow self.try_fold(0, move |i, x| { if predicate(x) { LoopState::Break(i) } else { LoopState::Continue(i + 1) } }).break_value() } /// Searches for an element in an iterator from the right, returning its /// index. /// /// `rposition()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, starting from the end, /// and if one of them returns `true`, then `rposition()` returns /// [`Some(index)`]. If all of them return `false`, it returns [`None`]. /// /// `rposition()` is short-circuiting; in other words, it will stop /// processing as soon as it finds a `true`. /// /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2)); /// /// assert_eq!(a.iter().rposition(|&x| x == 5), None); /// ``` /// /// Stopping at the first `true`: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert_eq!(iter.rposition(|&x| x == 2), Some(1)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&1)); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn rposition<P>(&mut self, mut predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool, Self: Sized + ExactSizeIterator + DoubleEndedIterator { // No need for an overflow check here, because `ExactSizeIterator` // implies that the number of elements fits into a `usize`. let n = self.len(); self.try_rfold(n, move |i, x| { let i = i - 1; if predicate(x) { LoopState::Break(i) } else { LoopState::Continue(i) } }).break_value() } /// Returns the maximum element of an iterator. /// /// If several elements are equally maximum, the last element is /// returned. If the iterator is empty, [`None`] is returned. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// let b: Vec<u32> = Vec::new(); /// /// assert_eq!(a.iter().max(), Some(&3)); /// assert_eq!(b.iter().max(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn max(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord { self.max_by(Ord::cmp) } /// Returns the minimum element of an iterator. /// /// If several elements are equally minimum, the first element is /// returned. If the iterator is empty, [`None`] is returned. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// let b: Vec<u32> = Vec::new(); /// /// assert_eq!(a.iter().min(), Some(&1)); /// assert_eq!(b.iter().min(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn min(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord { self.min_by(Ord::cmp) } /// Returns the element that gives the maximum value from the /// specified function. /// /// If several elements are equally maximum, the last element is /// returned. If the iterator is empty, [`None`] is returned. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// ``` /// let a = [-3_i32, 0, 1, 5, -10]; /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10); /// ``` #[inline] #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] fn max_by_key<B: Ord, F>(self, mut f: F) -> Option<Self::Item> where Self: Sized, F: FnMut(&Self::Item) -> B, { // switch to y even if it is only equal, to preserve stability. select_fold1(self.map(|x| (f(&x), x)), |(x_p, _), (y_p, _)| x_p <= y_p).map(|(_, x)| x) } /// Returns the element that gives the maximum value with respect to the /// specified comparison function. /// /// If several elements are equally maximum, the last element is /// returned. If the iterator is empty, [`None`] is returned. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// ``` /// let a = [-3_i32, 0, 1, 5, -10]; /// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5); /// ``` #[inline] #[stable(feature = "iter_max_by", since = "1.15.0")] fn max_by<F>(self, mut compare: F) -> Option<Self::Item> where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, { // switch to y even if it is only equal, to preserve stability. select_fold1(self, |x, y| compare(x, y) != Ordering::Greater) } /// Returns the element that gives the minimum value from the /// specified function. /// /// If several elements are equally minimum, the first element is /// returned. If the iterator is empty, [`None`] is returned. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// ``` /// let a = [-3_i32, 0, 1, 5, -10]; /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0); /// ``` #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] fn min_by_key<B: Ord, F>(self, mut f: F) -> Option<Self::Item> where Self: Sized, F: FnMut(&Self::Item) -> B, { // only switch to y if it is strictly smaller, to preserve stability. select_fold1(self.map(|x| (f(&x), x)), |(x_p, _), (y_p, _)| x_p > y_p).map(|(_, x)| x) } /// Returns the element that gives the minimum value with respect to the /// specified comparison function. /// /// If several elements are equally minimum, the first element is /// returned. If the iterator is empty, [`None`] is returned. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// ``` /// let a = [-3_i32, 0, 1, 5, -10]; /// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10); /// ``` #[inline] #[stable(feature = "iter_min_by", since = "1.15.0")] fn min_by<F>(self, mut compare: F) -> Option<Self::Item> where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, { // only switch to y if it is strictly smaller, to preserve stability. select_fold1(self, |x, y| compare(x, y) == Ordering::Greater) } /// Reverses an iterator's direction. /// /// Usually, iterators iterate from left to right. After using `rev()`, /// an iterator will instead iterate from right to left. /// /// This is only possible if the iterator has an end, so `rev()` only /// works on [`DoubleEndedIterator`]s. /// /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html /// /// # Examples /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().rev(); /// /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), Some(&1)); /// /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn rev(self) -> Rev<Self> where Self: Sized + DoubleEndedIterator { Rev::new(self) } /// Converts an iterator of pairs into a pair of containers. /// /// `unzip()` consumes an entire iterator of pairs, producing two /// collections: one from the left elements of the pairs, and one /// from the right elements. /// /// This function is, in some sense, the opposite of [`zip`]. /// /// [`zip`]: #method.zip /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [(1, 2), (3, 4)]; /// /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip(); /// /// assert_eq!(left, [1, 3]); /// assert_eq!(right, [2, 4]); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Sized + Iterator<Item=(A, B)>, { let mut ts: FromA = Default::default(); let mut us: FromB = Default::default(); self.for_each(|(t, u)| { ts.extend(Some(t)); us.extend(Some(u)); }); (ts, us) } /// Creates an iterator which copies all of its elements. /// /// This is useful when you have an iterator over `&T`, but you need an /// iterator over `T`. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let v_cloned: Vec<_> = a.iter().copied().collect(); /// /// // copied is the same as .map(|&x| x) /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); /// /// assert_eq!(v_cloned, vec![1, 2, 3]); /// assert_eq!(v_map, vec![1, 2, 3]); /// ``` #[stable(feature = "iter_copied", since = "1.36.0")] fn copied<'a, T: 'a>(self) -> Copied<Self> where Self: Sized + Iterator<Item=&'a T>, T: Copy { Copied::new(self) } /// Creates an iterator which [`clone`]s all of its elements. /// /// This is useful when you have an iterator over `&T`, but you need an /// iterator over `T`. /// /// [`clone`]: ../../std/clone/trait.Clone.html#tymethod.clone /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let v_cloned: Vec<_> = a.iter().cloned().collect(); /// /// // cloned is the same as .map(|&x| x), for integers /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); /// /// assert_eq!(v_cloned, vec![1, 2, 3]); /// assert_eq!(v_map, vec![1, 2, 3]); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn cloned<'a, T: 'a>(self) -> Cloned<Self> where Self: Sized + Iterator<Item=&'a T>, T: Clone { Cloned::new(self) } /// Repeats an iterator endlessly. /// /// Instead of stopping at [`None`], the iterator will instead start again, /// from the beginning. After iterating again, it will start at the /// beginning again. And again. And again. Forever. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut it = a.iter().cycle(); /// /// assert_eq!(it.next(), Some(&1)); /// assert_eq!(it.next(), Some(&2)); /// assert_eq!(it.next(), Some(&3)); /// assert_eq!(it.next(), Some(&1)); /// assert_eq!(it.next(), Some(&2)); /// assert_eq!(it.next(), Some(&3)); /// assert_eq!(it.next(), Some(&1)); /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[inline] fn cycle(self) -> Cycle<Self> where Self: Sized + Clone { Cycle::new(self) } /// Sums the elements of an iterator. /// /// Takes each element, adds them together, and returns the result. /// /// An empty iterator returns the zero value of the type. /// /// # Panics /// /// When calling `sum()` and a primitive integer type is being returned, this /// method will panic if the computation overflows and debug assertions are /// enabled. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// let sum: i32 = a.iter().sum(); /// /// assert_eq!(sum, 6); /// ``` #[stable(feature = "iter_arith", since = "1.11.0")] fn sum<S>(self) -> S where Self: Sized, S: Sum<Self::Item>, { Sum::sum(self) } /// Iterates over the entire iterator, multiplying all the elements /// /// An empty iterator returns the one value of the type. /// /// # Panics /// /// When calling `product()` and a primitive integer type is being returned, /// method will panic if the computation overflows and debug assertions are /// enabled. /// /// # Examples /// /// ``` /// fn factorial(n: u32) -> u32 { /// (1..=n).product() /// } /// assert_eq!(factorial(0), 1); /// assert_eq!(factorial(1), 1); /// assert_eq!(factorial(5), 120); /// ``` #[stable(feature = "iter_arith", since = "1.11.0")] fn product<P>(self) -> P where Self: Sized, P: Product<Self::Item>, { Product::product(self) } /// Lexicographically compares the elements of this `Iterator` with those /// of another. #[stable(feature = "iter_order", since = "1.5.0")] fn cmp<I>(mut self, other: I) -> Ordering where I: IntoIterator<Item = Self::Item>, Self::Item: Ord, Self: Sized, { let mut other = other.into_iter(); loop { let x = match self.next() { None => if other.next().is_none() { return Ordering::Equal } else { return Ordering::Less }, Some(val) => val, }; let y = match other.next() { None => return Ordering::Greater, Some(val) => val, }; match x.cmp(&y) { Ordering::Equal => (), non_eq => return non_eq, } } } /// Lexicographically compares the elements of this `Iterator` with those /// of another. #[stable(feature = "iter_order", since = "1.5.0")] fn partial_cmp<I>(mut self, other: I) -> Option<Ordering> where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized, { let mut other = other.into_iter(); loop { let x = match self.next() { None => if other.next().is_none() { return Some(Ordering::Equal) } else { return Some(Ordering::Less) }, Some(val) => val, }; let y = match other.next() { None => return Some(Ordering::Greater), Some(val) => val, }; match x.partial_cmp(&y) { Some(Ordering::Equal) => (), non_eq => return non_eq, } } } /// Determines if the elements of this `Iterator` are equal to those of /// another. #[stable(feature = "iter_order", since = "1.5.0")] fn eq<I>(mut self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item>, Self: Sized, { let mut other = other.into_iter(); loop { let x = match self.next() { None => return other.next().is_none(), Some(val) => val, }; let y = match other.next() { None => return false, Some(val) => val, }; if x != y { return false } } } /// Determines if the elements of this `Iterator` are unequal to those of /// another. #[stable(feature = "iter_order", since = "1.5.0")] fn ne<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item>, Self: Sized, { !self.eq(other) } /// Determines if the elements of this `Iterator` are lexicographically /// less than those of another. #[stable(feature = "iter_order", since = "1.5.0")] fn lt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized, { self.partial_cmp(other) == Some(Ordering::Less) } /// Determines if the elements of this `Iterator` are lexicographically /// less or equal to those of another. #[stable(feature = "iter_order", since = "1.5.0")] fn le<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized, { match self.partial_cmp(other) { Some(Ordering::Less) | Some(Ordering::Equal) => true, _ => false, } } /// Determines if the elements of this `Iterator` are lexicographically /// greater than those of another. #[stable(feature = "iter_order", since = "1.5.0")] fn gt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized, { self.partial_cmp(other) == Some(Ordering::Greater) } /// Determines if the elements of this `Iterator` are lexicographically /// greater than or equal to those of another. #[stable(feature = "iter_order", since = "1.5.0")] fn ge<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized, { match self.partial_cmp(other) { Some(Ordering::Greater) | Some(Ordering::Equal) => true, _ => false, } } /// Checks if the elements of this iterator are sorted. /// /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the /// iterator yields exactly zero or one element, `true` is returned. /// /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition /// implies that this function returns `false` if any two consecutive items are not /// comparable. /// /// # Examples /// /// ``` /// #![feature(is_sorted)] /// /// assert!([1, 2, 2, 9].iter().is_sorted()); /// assert!(![1, 3, 2, 4].iter().is_sorted()); /// assert!([0].iter().is_sorted()); /// assert!(std::iter::empty::<i32>().is_sorted()); /// assert!(![0.0, 1.0, std::f32::NAN].iter().is_sorted()); /// ``` #[inline] #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] fn is_sorted(self) -> bool where Self: Sized, Self::Item: PartialOrd, { self.is_sorted_by(|a, b| a.partial_cmp(b)) } /// Checks if the elements of this iterator are sorted using the given comparator function. /// /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` /// function to determine the ordering of two elements. Apart from that, it's equivalent to /// [`is_sorted`]; see its documentation for more information. /// /// [`is_sorted`]: trait.Iterator.html#method.is_sorted #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] fn is_sorted_by<F>(mut self, mut compare: F) -> bool where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering> { let mut last = match self.next() { Some(e) => e, None => return true, }; while let Some(curr) = self.next() { if compare(&last, &curr) .map(|o| o == Ordering::Greater) .unwrap_or(true) { return false; } last = curr; } true } /// Checks if the elements of this iterator are sorted using the given key extraction /// function. /// /// Instead of comparing the iterator's elements directly, this function compares the keys of /// the elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see /// its documentation for more information. /// /// [`is_sorted`]: trait.Iterator.html#method.is_sorted /// /// # Examples /// /// ``` /// #![feature(is_sorted)] /// /// assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len())); /// assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs())); /// ``` #[inline] #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] fn is_sorted_by_key<F, K>(self, mut f: F) -> bool where Self: Sized, F: FnMut(&Self::Item) -> K, K: PartialOrd { self.is_sorted_by(|a, b| f(a).partial_cmp(&f(b))) } } /// Select an element from an iterator based on the given "comparison" /// function. /// /// This is an idiosyncratic helper to try to factor out the /// commonalities of {max,min}{,_by}. In particular, this avoids /// having to implement optimizations several times. #[inline] fn select_fold1<I, F>(mut it: I, mut f: F) -> Option<I::Item> where I: Iterator, F: FnMut(&I::Item, &I::Item) -> bool, { // start with the first element as our selection. This avoids // having to use `Option`s inside the loop, translating to a // sizeable performance gain (6x in one case). it.next().map(|first| { it.fold(first, |sel, x| if f(&sel, &x) { x } else { sel }) }) } #[stable(feature = "rust1", since = "1.0.0")] impl<I: Iterator + ?Sized> Iterator for &mut I { type Item = I::Item; fn next(&mut self) -> Option<I::Item> { (**self).next() } fn size_hint(&self) -> (usize, Option<usize>) { (**self).size_hint() } fn nth(&mut self, n: usize) -> Option<Self::Item> { (**self).nth(n) } }