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//! Utilities for formatting and printing strings. #![stable(feature = "rust1", since = "1.0.0")] use crate::cell::{UnsafeCell, Cell, RefCell, Ref, RefMut}; use crate::marker::PhantomData; use crate::mem; use crate::num::flt2dec; use crate::ops::Deref; use crate::result; use crate::slice; use crate::str; mod float; mod num; mod builders; #[stable(feature = "fmt_flags_align", since = "1.28.0")] /// Possible alignments returned by `Formatter::align` #[derive(Debug)] pub enum Alignment { #[stable(feature = "fmt_flags_align", since = "1.28.0")] /// Indication that contents should be left-aligned. Left, #[stable(feature = "fmt_flags_align", since = "1.28.0")] /// Indication that contents should be right-aligned. Right, #[stable(feature = "fmt_flags_align", since = "1.28.0")] /// Indication that contents should be center-aligned. Center, } #[stable(feature = "debug_builders", since = "1.2.0")] pub use self::builders::{DebugStruct, DebugTuple, DebugSet, DebugList, DebugMap}; #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "0")] #[doc(hidden)] pub mod rt { pub mod v1; } /// The type returned by formatter methods. /// /// # Examples /// /// ``` /// use std::fmt; /// /// #[derive(Debug)] /// struct Triangle { /// a: f32, /// b: f32, /// c: f32 /// } /// /// impl fmt::Display for Triangle { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// write!(f, "({}, {}, {})", self.a, self.b, self.c) /// } /// } /// /// let pythagorean_triple = Triangle { a: 3.0, b: 4.0, c: 5.0 }; /// /// println!("{}", pythagorean_triple); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub type Result = result::Result<(), Error>; /// The error type which is returned from formatting a message into a stream. /// /// This type does not support transmission of an error other than that an error /// occurred. Any extra information must be arranged to be transmitted through /// some other means. /// /// An important thing to remember is that the type `fmt::Error` should not be /// confused with [`std::io::Error`] or [`std::error::Error`], which you may also /// have in scope. /// /// [`std::io::Error`]: ../../std/io/struct.Error.html /// [`std::error::Error`]: ../../std/error/trait.Error.html /// /// # Examples /// /// ```rust /// use std::fmt::{self, write}; /// /// let mut output = String::new(); /// if let Err(fmt::Error) = write(&mut output, format_args!("Hello {}!", "world")) { /// panic!("An error occurred"); /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)] pub struct Error; /// A collection of methods that are required to format a message into a stream. /// /// This trait is the type which this modules requires when formatting /// information. This is similar to the standard library's [`io::Write`] trait, /// but it is only intended for use in libcore. /// /// This trait should generally not be implemented by consumers of the standard /// library. The [`write!`] macro accepts an instance of [`io::Write`], and the /// [`io::Write`] trait is favored over implementing this trait. /// /// [`write!`]: ../../std/macro.write.html /// [`io::Write`]: ../../std/io/trait.Write.html #[stable(feature = "rust1", since = "1.0.0")] pub trait Write { /// Writes a slice of bytes into this writer, returning whether the write /// succeeded. /// /// This method can only succeed if the entire byte slice was successfully /// written, and this method will not return until all data has been /// written or an error occurs. /// /// # Errors /// /// This function will return an instance of [`Error`] on error. /// /// [`Error`]: struct.Error.html /// /// # Examples /// /// ``` /// use std::fmt::{Error, Write}; /// /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> { /// f.write_str(s) /// } /// /// let mut buf = String::new(); /// writer(&mut buf, "hola").unwrap(); /// assert_eq!(&buf, "hola"); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn write_str(&mut self, s: &str) -> Result; /// Writes a [`char`] into this writer, returning whether the write succeeded. /// /// A single [`char`] may be encoded as more than one byte. /// This method can only succeed if the entire byte sequence was successfully /// written, and this method will not return until all data has been /// written or an error occurs. /// /// # Errors /// /// This function will return an instance of [`Error`] on error. /// /// [`char`]: ../../std/primitive.char.html /// [`Error`]: struct.Error.html /// /// # Examples /// /// ``` /// use std::fmt::{Error, Write}; /// /// fn writer<W: Write>(f: &mut W, c: char) -> Result<(), Error> { /// f.write_char(c) /// } /// /// let mut buf = String::new(); /// writer(&mut buf, 'a').unwrap(); /// writer(&mut buf, 'b').unwrap(); /// assert_eq!(&buf, "ab"); /// ``` #[stable(feature = "fmt_write_char", since = "1.1.0")] fn write_char(&mut self, c: char) -> Result { self.write_str(c.encode_utf8(&mut [0; 4])) } /// Glue for usage of the [`write!`] macro with implementors of this trait. /// /// This method should generally not be invoked manually, but rather through /// the [`write!`] macro itself. /// /// [`write!`]: ../../std/macro.write.html /// /// # Examples /// /// ``` /// use std::fmt::{Error, Write}; /// /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> { /// f.write_fmt(format_args!("{}", s)) /// } /// /// let mut buf = String::new(); /// writer(&mut buf, "world").unwrap(); /// assert_eq!(&buf, "world"); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn write_fmt(mut self: &mut Self, args: Arguments<'_>) -> Result { write(&mut self, args) } } #[stable(feature = "fmt_write_blanket_impl", since = "1.4.0")] impl<W: Write + ?Sized> Write for &mut W { fn write_str(&mut self, s: &str) -> Result { (**self).write_str(s) } fn write_char(&mut self, c: char) -> Result { (**self).write_char(c) } fn write_fmt(&mut self, args: Arguments<'_>) -> Result { (**self).write_fmt(args) } } /// Configuration for formatting. /// /// A `Formatter` represents various options related to formatting. Users do not /// construct `Formatter`s directly; a mutable reference to one is passed to /// the `fmt` method of all formatting traits, like [`Debug`] and [`Display`]. /// /// To interact with a `Formatter`, you'll call various methods to change the /// various options related to formatting. For examples, please see the /// documentation of the methods defined on `Formatter` below. /// /// [`Debug`]: trait.Debug.html /// [`Display`]: trait.Display.html #[allow(missing_debug_implementations)] #[stable(feature = "rust1", since = "1.0.0")] pub struct Formatter<'a> { flags: u32, fill: char, align: rt::v1::Alignment, width: Option<usize>, precision: Option<usize>, buf: &'a mut (dyn Write+'a), curarg: slice::Iter<'a, ArgumentV1<'a>>, args: &'a [ArgumentV1<'a>], } // NB. Argument is essentially an optimized partially applied formatting function, // equivalent to `exists T.(&T, fn(&T, &mut Formatter<'_>) -> Result`. struct Void { _priv: (), /// Erases all oibits, because `Void` erases the type of the object that /// will be used to produce formatted output. Since we do not know what /// oibits the real types have (and they can have any or none), we need to /// take the most conservative approach and forbid all oibits. /// /// It was added after #45197 showed that one could share a `!Sync` /// object across threads by passing it into `format_args!`. _oibit_remover: PhantomData<*mut dyn Fn()>, } /// This struct represents the generic "argument" which is taken by the Xprintf /// family of functions. It contains a function to format the given value. At /// compile time it is ensured that the function and the value have the correct /// types, and then this struct is used to canonicalize arguments to one type. #[derive(Copy, Clone)] #[allow(missing_debug_implementations)] #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "0")] #[doc(hidden)] pub struct ArgumentV1<'a> { value: &'a Void, formatter: fn(&Void, &mut Formatter<'_>) -> Result, } impl<'a> ArgumentV1<'a> { #[inline(never)] fn show_usize(x: &usize, f: &mut Formatter<'_>) -> Result { Display::fmt(x, f) } #[doc(hidden)] #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "0")] pub fn new<'b, T>(x: &'b T, f: fn(&T, &mut Formatter<'_>) -> Result) -> ArgumentV1<'b> { unsafe { ArgumentV1 { formatter: mem::transmute(f), value: mem::transmute(x) } } } #[doc(hidden)] #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "0")] pub fn from_usize(x: &usize) -> ArgumentV1<'_> { ArgumentV1::new(x, ArgumentV1::show_usize) } fn as_usize(&self) -> Option<usize> { if self.formatter as usize == ArgumentV1::show_usize as usize { Some(unsafe { *(self.value as *const _ as *const usize) }) } else { None } } } // flags available in the v1 format of format_args #[derive(Copy, Clone)] enum FlagV1 { SignPlus, SignMinus, Alternate, SignAwareZeroPad, DebugLowerHex, DebugUpperHex } impl<'a> Arguments<'a> { /// When using the format_args!() macro, this function is used to generate the /// Arguments structure. #[doc(hidden)] #[inline] #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "0")] pub fn new_v1(pieces: &'a [&'a str], args: &'a [ArgumentV1<'a>]) -> Arguments<'a> { Arguments { pieces, fmt: None, args, } } /// This function is used to specify nonstandard formatting parameters. /// The `pieces` array must be at least as long as `fmt` to construct /// a valid Arguments structure. Also, any `Count` within `fmt` that is /// `CountIsParam` or `CountIsNextParam` has to point to an argument /// created with `argumentusize`. However, failing to do so doesn't cause /// unsafety, but will ignore invalid . #[doc(hidden)] #[inline] #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "0")] pub fn new_v1_formatted(pieces: &'a [&'a str], args: &'a [ArgumentV1<'a>], fmt: &'a [rt::v1::Argument]) -> Arguments<'a> { Arguments { pieces, fmt: Some(fmt), args, } } /// Estimates the length of the formatted text. /// /// This is intended to be used for setting initial `String` capacity /// when using `format!`. Note: this is neither the lower nor upper bound. #[doc(hidden)] #[inline] #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "0")] pub fn estimated_capacity(&self) -> usize { let pieces_length: usize = self.pieces.iter() .map(|x| x.len()).sum(); if self.args.is_empty() { pieces_length } else if self.pieces[0] == "" && pieces_length < 16 { // If the format string starts with an argument, // don't preallocate anything, unless length // of pieces is significant. 0 } else { // There are some arguments, so any additional push // will reallocate the string. To avoid that, // we're "pre-doubling" the capacity here. pieces_length.checked_mul(2).unwrap_or(0) } } } /// This structure represents a safely precompiled version of a format string /// and its arguments. This cannot be generated at runtime because it cannot /// safely be done, so no constructors are given and the fields are private /// to prevent modification. /// /// The [`format_args!`] macro will safely create an instance of this structure. /// The macro validates the format string at compile-time so usage of the /// [`write`] and [`format`] functions can be safely performed. /// /// You can use the `Arguments<'a>` that [`format_args!`] returns in `Debug` /// and `Display` contexts as seen below. The example also shows that `Debug` /// and `Display` format to the same thing: the interpolated format string /// in `format_args!`. /// /// ```rust /// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2)); /// let display = format!("{}", format_args!("{} foo {:?}", 1, 2)); /// assert_eq!("1 foo 2", display); /// assert_eq!(display, debug); /// ``` /// /// [`format_args!`]: ../../std/macro.format_args.html /// [`format`]: ../../std/fmt/fn.format.html /// [`write`]: ../../std/fmt/fn.write.html #[stable(feature = "rust1", since = "1.0.0")] #[derive(Copy, Clone)] pub struct Arguments<'a> { // Format string pieces to print. pieces: &'a [&'a str], // Placeholder specs, or `None` if all specs are default (as in "{}{}"). fmt: Option<&'a [rt::v1::Argument]>, // Dynamic arguments for interpolation, to be interleaved with string // pieces. (Every argument is preceded by a string piece.) args: &'a [ArgumentV1<'a>], } #[stable(feature = "rust1", since = "1.0.0")] impl Debug for Arguments<'_> { fn fmt(&self, fmt: &mut Formatter<'_>) -> Result { Display::fmt(self, fmt) } } #[stable(feature = "rust1", since = "1.0.0")] impl Display for Arguments<'_> { fn fmt(&self, fmt: &mut Formatter<'_>) -> Result { write(fmt.buf, *self) } } /// `?` formatting. /// /// `Debug` should format the output in a programmer-facing, debugging context. /// /// Generally speaking, you should just `derive` a `Debug` implementation. /// /// When used with the alternate format specifier `#?`, the output is pretty-printed. /// /// For more information on formatters, see [the module-level documentation][module]. /// /// [module]: ../../std/fmt/index.html /// /// This trait can be used with `#[derive]` if all fields implement `Debug`. When /// `derive`d for structs, it will use the name of the `struct`, then `{`, then a /// comma-separated list of each field's name and `Debug` value, then `}`. For /// `enum`s, it will use the name of the variant and, if applicable, `(`, then the /// `Debug` values of the fields, then `)`. /// /// # Examples /// /// Deriving an implementation: /// /// ``` /// #[derive(Debug)] /// struct Point { /// x: i32, /// y: i32, /// } /// /// let origin = Point { x: 0, y: 0 }; /// /// println!("The origin is: {:?}", origin); /// ``` /// /// Manually implementing: /// /// ``` /// use std::fmt; /// /// struct Point { /// x: i32, /// y: i32, /// } /// /// impl fmt::Debug for Point { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// write!(f, "Point {{ x: {}, y: {} }}", self.x, self.y) /// } /// } /// /// let origin = Point { x: 0, y: 0 }; /// /// println!("The origin is: {:?}", origin); /// ``` /// /// This outputs: /// /// ```text /// The origin is: Point { x: 0, y: 0 } /// ``` /// /// There are a number of `debug_*` methods on [`Formatter`] to help you with manual /// implementations, such as [`debug_struct`][debug_struct]. /// /// `Debug` implementations using either `derive` or the debug builder API /// on [`Formatter`] support pretty-printing using the alternate flag: `{:#?}`. /// /// [debug_struct]: ../../std/fmt/struct.Formatter.html#method.debug_struct /// [`Formatter`]: ../../std/fmt/struct.Formatter.html /// /// Pretty-printing with `#?`: /// /// ``` /// #[derive(Debug)] /// struct Point { /// x: i32, /// y: i32, /// } /// /// let origin = Point { x: 0, y: 0 }; /// /// println!("The origin is: {:#?}", origin); /// ``` /// /// This outputs: /// /// ```text /// The origin is: Point { /// x: 0, /// y: 0 /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[rustc_on_unimplemented( on(crate_local, label="`{Self}` cannot be formatted using `{{:?}}`", note="add `#[derive(Debug)]` or manually implement `{Debug}`"), message="`{Self}` doesn't implement `{Debug}`", label="`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{Debug}`", )] #[doc(alias = "{:?}")] #[lang = "debug_trait"] pub trait Debug { /// Formats the value using the given formatter. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Position { /// longitude: f32, /// latitude: f32, /// } /// /// impl fmt::Debug for Position { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// write!(f, "({:?}, {:?})", self.longitude, self.latitude) /// } /// } /// /// assert_eq!("(1.987, 2.983)".to_owned(), /// format!("{:?}", Position { longitude: 1.987, latitude: 2.983, })); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn fmt(&self, f: &mut Formatter<'_>) -> Result; } /// Format trait for an empty format, `{}`. /// /// `Display` is similar to [`Debug`][debug], but `Display` is for user-facing /// output, and so cannot be derived. /// /// [debug]: trait.Debug.html /// /// For more information on formatters, see [the module-level documentation][module]. /// /// [module]: ../../std/fmt/index.html /// /// # Examples /// /// Implementing `Display` on a type: /// /// ``` /// use std::fmt; /// /// struct Point { /// x: i32, /// y: i32, /// } /// /// impl fmt::Display for Point { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// write!(f, "({}, {})", self.x, self.y) /// } /// } /// /// let origin = Point { x: 0, y: 0 }; /// /// println!("The origin is: {}", origin); /// ``` #[rustc_on_unimplemented( on( _Self="std::path::Path", label="`{Self}` cannot be formatted with the default formatter; call `.display()` on it", note="call `.display()` or `.to_string_lossy()` to safely print paths, \ as they may contain non-Unicode data" ), message="`{Self}` doesn't implement `{Display}`", label="`{Self}` cannot be formatted with the default formatter", note="in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead", )] #[doc(alias = "{}")] #[stable(feature = "rust1", since = "1.0.0")] pub trait Display { /// Formats the value using the given formatter. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Position { /// longitude: f32, /// latitude: f32, /// } /// /// impl fmt::Display for Position { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// write!(f, "({}, {})", self.longitude, self.latitude) /// } /// } /// /// assert_eq!("(1.987, 2.983)".to_owned(), /// format!("{}", Position { longitude: 1.987, latitude: 2.983, })); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn fmt(&self, f: &mut Formatter<'_>) -> Result; } /// `o` formatting. /// /// The `Octal` trait should format its output as a number in base-8. /// /// For primitive signed integers (`i8` to `i128`, and `isize`), /// negative values are formatted as the two’s complement representation. /// /// The alternate flag, `#`, adds a `0o` in front of the output. /// /// For more information on formatters, see [the module-level documentation][module]. /// /// [module]: ../../std/fmt/index.html /// /// # Examples /// /// Basic usage with `i32`: /// /// ``` /// let x = 42; // 42 is '52' in octal /// /// assert_eq!(format!("{:o}", x), "52"); /// assert_eq!(format!("{:#o}", x), "0o52"); /// /// assert_eq!(format!("{:o}", -16), "37777777760"); /// ``` /// /// Implementing `Octal` on a type: /// /// ``` /// use std::fmt; /// /// struct Length(i32); /// /// impl fmt::Octal for Length { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// let val = self.0; /// /// write!(f, "{:o}", val) // delegate to i32's implementation /// } /// } /// /// let l = Length(9); /// /// println!("l as octal is: {:o}", l); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub trait Octal { /// Formats the value using the given formatter. #[stable(feature = "rust1", since = "1.0.0")] fn fmt(&self, f: &mut Formatter<'_>) -> Result; } /// `b` formatting. /// /// The `Binary` trait should format its output as a number in binary. /// /// For primitive signed integers ([`i8`] to [`i128`], and [`isize`]), /// negative values are formatted as the two’s complement representation. /// /// The alternate flag, `#`, adds a `0b` in front of the output. /// /// For more information on formatters, see [the module-level documentation][module]. /// /// # Examples /// /// Basic usage with [`i32`]: /// /// ``` /// let x = 42; // 42 is '101010' in binary /// /// assert_eq!(format!("{:b}", x), "101010"); /// assert_eq!(format!("{:#b}", x), "0b101010"); /// /// assert_eq!(format!("{:b}", -16), "11111111111111111111111111110000"); /// ``` /// /// Implementing `Binary` on a type: /// /// ``` /// use std::fmt; /// /// struct Length(i32); /// /// impl fmt::Binary for Length { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// let val = self.0; /// /// write!(f, "{:b}", val) // delegate to i32's implementation /// } /// } /// /// let l = Length(107); /// /// println!("l as binary is: {:b}", l); /// ``` /// /// [module]: ../../std/fmt/index.html /// [`i8`]: ../../std/primitive.i8.html /// [`i128`]: ../../std/primitive.i128.html /// [`isize`]: ../../std/primitive.isize.html /// [`i32`]: ../../std/primitive.i32.html #[stable(feature = "rust1", since = "1.0.0")] pub trait Binary { /// Formats the value using the given formatter. #[stable(feature = "rust1", since = "1.0.0")] fn fmt(&self, f: &mut Formatter<'_>) -> Result; } /// `x` formatting. /// /// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f` /// in lower case. /// /// For primitive signed integers (`i8` to `i128`, and `isize`), /// negative values are formatted as the two’s complement representation. /// /// The alternate flag, `#`, adds a `0x` in front of the output. /// /// For more information on formatters, see [the module-level documentation][module]. /// /// [module]: ../../std/fmt/index.html /// /// # Examples /// /// Basic usage with `i32`: /// /// ``` /// let x = 42; // 42 is '2a' in hex /// /// assert_eq!(format!("{:x}", x), "2a"); /// assert_eq!(format!("{:#x}", x), "0x2a"); /// /// assert_eq!(format!("{:x}", -16), "fffffff0"); /// ``` /// /// Implementing `LowerHex` on a type: /// /// ``` /// use std::fmt; /// /// struct Length(i32); /// /// impl fmt::LowerHex for Length { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// let val = self.0; /// /// write!(f, "{:x}", val) // delegate to i32's implementation /// } /// } /// /// let l = Length(9); /// /// println!("l as hex is: {:x}", l); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub trait LowerHex { /// Formats the value using the given formatter. #[stable(feature = "rust1", since = "1.0.0")] fn fmt(&self, f: &mut Formatter<'_>) -> Result; } /// `X` formatting. /// /// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F` /// in upper case. /// /// For primitive signed integers (`i8` to `i128`, and `isize`), /// negative values are formatted as the two’s complement representation. /// /// The alternate flag, `#`, adds a `0x` in front of the output. /// /// For more information on formatters, see [the module-level documentation][module]. /// /// [module]: ../../std/fmt/index.html /// /// # Examples /// /// Basic usage with `i32`: /// /// ``` /// let x = 42; // 42 is '2A' in hex /// /// assert_eq!(format!("{:X}", x), "2A"); /// assert_eq!(format!("{:#X}", x), "0x2A"); /// /// assert_eq!(format!("{:X}", -16), "FFFFFFF0"); /// ``` /// /// Implementing `UpperHex` on a type: /// /// ``` /// use std::fmt; /// /// struct Length(i32); /// /// impl fmt::UpperHex for Length { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// let val = self.0; /// /// write!(f, "{:X}", val) // delegate to i32's implementation /// } /// } /// /// let l = Length(9); /// /// println!("l as hex is: {:X}", l); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub trait UpperHex { /// Formats the value using the given formatter. #[stable(feature = "rust1", since = "1.0.0")] fn fmt(&self, f: &mut Formatter<'_>) -> Result; } /// `p` formatting. /// /// The `Pointer` trait should format its output as a memory location. This is commonly presented /// as hexadecimal. /// /// For more information on formatters, see [the module-level documentation][module]. /// /// [module]: ../../std/fmt/index.html /// /// # Examples /// /// Basic usage with `&i32`: /// /// ``` /// let x = &42; /// /// let address = format!("{:p}", x); // this produces something like '0x7f06092ac6d0' /// ``` /// /// Implementing `Pointer` on a type: /// /// ``` /// use std::fmt; /// /// struct Length(i32); /// /// impl fmt::Pointer for Length { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// // use `as` to convert to a `*const T`, which implements Pointer, which we can use /// /// write!(f, "{:p}", self as *const Length) /// } /// } /// /// let l = Length(42); /// /// println!("l is in memory here: {:p}", l); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub trait Pointer { /// Formats the value using the given formatter. #[stable(feature = "rust1", since = "1.0.0")] fn fmt(&self, f: &mut Formatter<'_>) -> Result; } /// `e` formatting. /// /// The `LowerExp` trait should format its output in scientific notation with a lower-case `e`. /// /// For more information on formatters, see [the module-level documentation][module]. /// /// [module]: ../../std/fmt/index.html /// /// # Examples /// /// Basic usage with `f64`: /// /// ``` /// let x = 42.0; // 42.0 is '4.2e1' in scientific notation /// /// assert_eq!(format!("{:e}", x), "4.2e1"); /// ``` /// /// Implementing `LowerExp` on a type: /// /// ``` /// use std::fmt; /// /// struct Length(i32); /// /// impl fmt::LowerExp for Length { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// let val = self.0; /// write!(f, "{}e1", val / 10) /// } /// } /// /// let l = Length(100); /// /// println!("l in scientific notation is: {:e}", l); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub trait LowerExp { /// Formats the value using the given formatter. #[stable(feature = "rust1", since = "1.0.0")] fn fmt(&self, f: &mut Formatter<'_>) -> Result; } /// `E` formatting. /// /// The `UpperExp` trait should format its output in scientific notation with an upper-case `E`. /// /// For more information on formatters, see [the module-level documentation][module]. /// /// [module]: ../../std/fmt/index.html /// /// # Examples /// /// Basic usage with `f64`: /// /// ``` /// let x = 42.0; // 42.0 is '4.2E1' in scientific notation /// /// assert_eq!(format!("{:E}", x), "4.2E1"); /// ``` /// /// Implementing `UpperExp` on a type: /// /// ``` /// use std::fmt; /// /// struct Length(i32); /// /// impl fmt::UpperExp for Length { /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { /// let val = self.0; /// write!(f, "{}E1", val / 10) /// } /// } /// /// let l = Length(100); /// /// println!("l in scientific notation is: {:E}", l); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub trait UpperExp { /// Formats the value using the given formatter. #[stable(feature = "rust1", since = "1.0.0")] fn fmt(&self, f: &mut Formatter<'_>) -> Result; } /// The `write` function takes an output stream, and an `Arguments` struct /// that can be precompiled with the `format_args!` macro. /// /// The arguments will be formatted according to the specified format string /// into the output stream provided. /// /// # Examples /// /// Basic usage: /// /// ``` /// use std::fmt; /// /// let mut output = String::new(); /// fmt::write(&mut output, format_args!("Hello {}!", "world")) /// .expect("Error occurred while trying to write in String"); /// assert_eq!(output, "Hello world!"); /// ``` /// /// Please note that using [`write!`] might be preferable. Example: /// /// ``` /// use std::fmt::Write; /// /// let mut output = String::new(); /// write!(&mut output, "Hello {}!", "world") /// .expect("Error occurred while trying to write in String"); /// assert_eq!(output, "Hello world!"); /// ``` /// /// [`write!`]: ../../std/macro.write.html #[stable(feature = "rust1", since = "1.0.0")] pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result { let mut formatter = Formatter { flags: 0, width: None, precision: None, buf: output, align: rt::v1::Alignment::Unknown, fill: ' ', args: args.args, curarg: args.args.iter(), }; let mut idx = 0; match args.fmt { None => { // We can use default formatting parameters for all arguments. for (arg, piece) in args.args.iter().zip(args.pieces.iter()) { formatter.buf.write_str(*piece)?; (arg.formatter)(arg.value, &mut formatter)?; idx += 1; } } Some(fmt) => { // Every spec has a corresponding argument that is preceded by // a string piece. for (arg, piece) in fmt.iter().zip(args.pieces.iter()) { formatter.buf.write_str(*piece)?; formatter.run(arg)?; idx += 1; } } } // There can be only one trailing string piece left. if let Some(piece) = args.pieces.get(idx) { formatter.buf.write_str(*piece)?; } Ok(()) } /// Padding after the end of something. Returned by `Formatter::padding`. #[must_use = "don't forget to write the post padding"] struct PostPadding { fill: char, padding: usize, } impl PostPadding { fn new(fill: char, padding: usize) -> PostPadding { PostPadding { fill, padding } } /// Write this post padding. fn write(self, buf: &mut dyn Write) -> Result { for _ in 0..self.padding { buf.write_char(self.fill)?; } Ok(()) } } impl<'a> Formatter<'a> { fn wrap_buf<'b, 'c, F>(&'b mut self, wrap: F) -> Formatter<'c> where 'b: 'c, F: FnOnce(&'b mut (dyn Write+'b)) -> &'c mut (dyn Write+'c) { Formatter { // We want to change this buf: wrap(self.buf), // And preserve these flags: self.flags, fill: self.fill, align: self.align, width: self.width, precision: self.precision, // These only exist in the struct for the `run` method, // which won’t be used together with this method. curarg: self.curarg.clone(), args: self.args, } } // First up is the collection of functions used to execute a format string // at runtime. This consumes all of the compile-time statics generated by // the format! syntax extension. fn run(&mut self, arg: &rt::v1::Argument) -> Result { // Fill in the format parameters into the formatter self.fill = arg.format.fill; self.align = arg.format.align; self.flags = arg.format.flags; self.width = self.getcount(&arg.format.width); self.precision = self.getcount(&arg.format.precision); // Extract the correct argument let value = match arg.position { rt::v1::Position::Next => { *self.curarg.next().unwrap() } rt::v1::Position::At(i) => self.args[i], }; // Then actually do some printing (value.formatter)(value.value, self) } fn getcount(&mut self, cnt: &rt::v1::Count) -> Option<usize> { match *cnt { rt::v1::Count::Is(n) => Some(n), rt::v1::Count::Implied => None, rt::v1::Count::Param(i) => { self.args[i].as_usize() } rt::v1::Count::NextParam => { self.curarg.next()?.as_usize() } } } // Helper methods used for padding and processing formatting arguments that // all formatting traits can use. /// Performs the correct padding for an integer which has already been /// emitted into a str. The str should *not* contain the sign for the /// integer, that will be added by this method. /// /// # Arguments /// /// * is_nonnegative - whether the original integer was either positive or zero. /// * prefix - if the '#' character (Alternate) is provided, this /// is the prefix to put in front of the number. /// * buf - the byte array that the number has been formatted into /// /// This function will correctly account for the flags provided as well as /// the minimum width. It will not take precision into account. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo { nb: i32 }; /// /// impl Foo { /// fn new(nb: i32) -> Foo { /// Foo { /// nb, /// } /// } /// } /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// // We need to remove "-" from the number output. /// let tmp = self.nb.abs().to_string(); /// /// formatter.pad_integral(self.nb > 0, "Foo ", &tmp) /// } /// } /// /// assert_eq!(&format!("{}", Foo::new(2)), "2"); /// assert_eq!(&format!("{}", Foo::new(-1)), "-1"); /// assert_eq!(&format!("{:#}", Foo::new(-1)), "-Foo 1"); /// assert_eq!(&format!("{:0>#8}", Foo::new(-1)), "00-Foo 1"); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn pad_integral(&mut self, is_nonnegative: bool, prefix: &str, buf: &str) -> Result { let mut width = buf.len(); let mut sign = None; if !is_nonnegative { sign = Some('-'); width += 1; } else if self.sign_plus() { sign = Some('+'); width += 1; } let prefix = if self.alternate() { width += prefix.chars().count(); Some(prefix) } else { None }; // Writes the sign if it exists, and then the prefix if it was requested #[inline(never)] fn write_prefix(f: &mut Formatter<'_>, sign: Option<char>, prefix: Option<&str>) -> Result { if let Some(c) = sign { f.buf.write_char(c)?; } if let Some(prefix) = prefix { f.buf.write_str(prefix) } else { Ok(()) } } // The `width` field is more of a `min-width` parameter at this point. match self.width { // If there's no minimum length requirements then we can just // write the bytes. None => { write_prefix(self, sign, prefix)?; self.buf.write_str(buf) } // Check if we're over the minimum width, if so then we can also // just write the bytes. Some(min) if width >= min => { write_prefix(self, sign, prefix)?; self.buf.write_str(buf) } // The sign and prefix goes before the padding if the fill character // is zero Some(min) if self.sign_aware_zero_pad() => { self.fill = '0'; self.align = rt::v1::Alignment::Right; write_prefix(self, sign, prefix)?; let post_padding = self.padding(min - width, rt::v1::Alignment::Right)?; self.buf.write_str(buf)?; post_padding.write(self.buf) } // Otherwise, the sign and prefix goes after the padding Some(min) => { let post_padding = self.padding(min - width, rt::v1::Alignment::Right)?; write_prefix(self, sign, prefix)?; self.buf.write_str(buf)?; post_padding.write(self.buf) } } } /// This function takes a string slice and emits it to the internal buffer /// after applying the relevant formatting flags specified. The flags /// recognized for generic strings are: /// /// * width - the minimum width of what to emit /// * fill/align - what to emit and where to emit it if the string /// provided needs to be padded /// * precision - the maximum length to emit, the string is truncated if it /// is longer than this length /// /// Notably this function ignores the `flag` parameters. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo; /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// formatter.pad("Foo") /// } /// } /// /// assert_eq!(&format!("{:<4}", Foo), "Foo "); /// assert_eq!(&format!("{:0>4}", Foo), "0Foo"); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn pad(&mut self, s: &str) -> Result { // Make sure there's a fast path up front if self.width.is_none() && self.precision.is_none() { return self.buf.write_str(s); } // The `precision` field can be interpreted as a `max-width` for the // string being formatted. let s = if let Some(max) = self.precision { // If our string is longer that the precision, then we must have // truncation. However other flags like `fill`, `width` and `align` // must act as always. if let Some((i, _)) = s.char_indices().nth(max) { // LLVM here can't prove that `..i` won't panic `&s[..i]`, but // we know that it can't panic. Use `get` + `unwrap_or` to avoid // `unsafe` and otherwise don't emit any panic-related code // here. s.get(..i).unwrap_or(&s) } else { &s } } else { &s }; // The `width` field is more of a `min-width` parameter at this point. match self.width { // If we're under the maximum length, and there's no minimum length // requirements, then we can just emit the string None => self.buf.write_str(s), // If we're under the maximum width, check if we're over the minimum // width, if so it's as easy as just emitting the string. Some(width) if s.chars().count() >= width => { self.buf.write_str(s) } // If we're under both the maximum and the minimum width, then fill // up the minimum width with the specified string + some alignment. Some(width) => { let align = rt::v1::Alignment::Left; let post_padding = self.padding(width - s.chars().count(), align)?; self.buf.write_str(s)?; post_padding.write(self.buf) } } } /// Write the pre-padding and return the unwritten post-padding. Callers are /// responsible for ensuring post-padding is written after the thing that is /// being padded. fn padding( &mut self, padding: usize, default: rt::v1::Alignment ) -> result::Result<PostPadding, Error> { let align = match self.align { rt::v1::Alignment::Unknown => default, _ => self.align }; let (pre_pad, post_pad) = match align { rt::v1::Alignment::Left => (0, padding), rt::v1::Alignment::Right | rt::v1::Alignment::Unknown => (padding, 0), rt::v1::Alignment::Center => (padding / 2, (padding + 1) / 2), }; for _ in 0..pre_pad { self.buf.write_char(self.fill)?; } Ok(PostPadding::new(self.fill, post_pad)) } /// Takes the formatted parts and applies the padding. /// Assumes that the caller already has rendered the parts with required precision, /// so that `self.precision` can be ignored. fn pad_formatted_parts(&mut self, formatted: &flt2dec::Formatted<'_>) -> Result { if let Some(mut width) = self.width { // for the sign-aware zero padding, we render the sign first and // behave as if we had no sign from the beginning. let mut formatted = formatted.clone(); let old_fill = self.fill; let old_align = self.align; let mut align = old_align; if self.sign_aware_zero_pad() { // a sign always goes first let sign = unsafe { str::from_utf8_unchecked(formatted.sign) }; self.buf.write_str(sign)?; // remove the sign from the formatted parts formatted.sign = b""; width = width.saturating_sub(sign.len()); align = rt::v1::Alignment::Right; self.fill = '0'; self.align = rt::v1::Alignment::Right; } // remaining parts go through the ordinary padding process. let len = formatted.len(); let ret = if width <= len { // no padding self.write_formatted_parts(&formatted) } else { let post_padding = self.padding(width - len, align)?; self.write_formatted_parts(&formatted)?; post_padding.write(self.buf) }; self.fill = old_fill; self.align = old_align; ret } else { // this is the common case and we take a shortcut self.write_formatted_parts(formatted) } } fn write_formatted_parts(&mut self, formatted: &flt2dec::Formatted<'_>) -> Result { fn write_bytes(buf: &mut dyn Write, s: &[u8]) -> Result { buf.write_str(unsafe { str::from_utf8_unchecked(s) }) } if !formatted.sign.is_empty() { write_bytes(self.buf, formatted.sign)?; } for part in formatted.parts { match *part { flt2dec::Part::Zero(mut nzeroes) => { const ZEROES: &str = // 64 zeroes "0000000000000000000000000000000000000000000000000000000000000000"; while nzeroes > ZEROES.len() { self.buf.write_str(ZEROES)?; nzeroes -= ZEROES.len(); } if nzeroes > 0 { self.buf.write_str(&ZEROES[..nzeroes])?; } } flt2dec::Part::Num(mut v) => { let mut s = [0; 5]; let len = part.len(); for c in s[..len].iter_mut().rev() { *c = b'0' + (v % 10) as u8; v /= 10; } write_bytes(self.buf, &s[..len])?; } flt2dec::Part::Copy(buf) => { write_bytes(self.buf, buf)?; } } } Ok(()) } /// Writes some data to the underlying buffer contained within this /// formatter. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo; /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// formatter.write_str("Foo") /// // This is equivalent to: /// // write!(formatter, "Foo") /// } /// } /// /// assert_eq!(&format!("{}", Foo), "Foo"); /// assert_eq!(&format!("{:0>8}", Foo), "Foo"); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn write_str(&mut self, data: &str) -> Result { self.buf.write_str(data) } /// Writes some formatted information into this instance. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo(i32); /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// formatter.write_fmt(format_args!("Foo {}", self.0)) /// } /// } /// /// assert_eq!(&format!("{}", Foo(-1)), "Foo -1"); /// assert_eq!(&format!("{:0>8}", Foo(2)), "Foo 2"); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result { write(self.buf, fmt) } /// Flags for formatting #[stable(feature = "rust1", since = "1.0.0")] #[rustc_deprecated(since = "1.24.0", reason = "use the `sign_plus`, `sign_minus`, `alternate`, \ or `sign_aware_zero_pad` methods instead")] pub fn flags(&self) -> u32 { self.flags } /// Character used as 'fill' whenever there is alignment. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo; /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// let c = formatter.fill(); /// if let Some(width) = formatter.width() { /// for _ in 0..width { /// write!(formatter, "{}", c)?; /// } /// Ok(()) /// } else { /// write!(formatter, "{}", c) /// } /// } /// } /// /// // We set alignment to the left with ">". /// assert_eq!(&format!("{:G>3}", Foo), "GGG"); /// assert_eq!(&format!("{:t>6}", Foo), "tttttt"); /// ``` #[stable(feature = "fmt_flags", since = "1.5.0")] pub fn fill(&self) -> char { self.fill } /// Flag indicating what form of alignment was requested. /// /// # Examples /// /// ``` /// extern crate core; /// /// use std::fmt::{self, Alignment}; /// /// struct Foo; /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// let s = if let Some(s) = formatter.align() { /// match s { /// Alignment::Left => "left", /// Alignment::Right => "right", /// Alignment::Center => "center", /// } /// } else { /// "into the void" /// }; /// write!(formatter, "{}", s) /// } /// } /// /// fn main() { /// assert_eq!(&format!("{:<}", Foo), "left"); /// assert_eq!(&format!("{:>}", Foo), "right"); /// assert_eq!(&format!("{:^}", Foo), "center"); /// assert_eq!(&format!("{}", Foo), "into the void"); /// } /// ``` #[stable(feature = "fmt_flags_align", since = "1.28.0")] pub fn align(&self) -> Option<Alignment> { match self.align { rt::v1::Alignment::Left => Some(Alignment::Left), rt::v1::Alignment::Right => Some(Alignment::Right), rt::v1::Alignment::Center => Some(Alignment::Center), rt::v1::Alignment::Unknown => None, } } /// Optionally specified integer width that the output should be. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo(i32); /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// if let Some(width) = formatter.width() { /// // If we received a width, we use it /// write!(formatter, "{:width$}", &format!("Foo({})", self.0), width = width) /// } else { /// // Otherwise we do nothing special /// write!(formatter, "Foo({})", self.0) /// } /// } /// } /// /// assert_eq!(&format!("{:10}", Foo(23)), "Foo(23) "); /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)"); /// ``` #[stable(feature = "fmt_flags", since = "1.5.0")] pub fn width(&self) -> Option<usize> { self.width } /// Optionally specified precision for numeric types. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo(f32); /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// if let Some(precision) = formatter.precision() { /// // If we received a precision, we use it. /// write!(formatter, "Foo({1:.*})", precision, self.0) /// } else { /// // Otherwise we default to 2. /// write!(formatter, "Foo({:.2})", self.0) /// } /// } /// } /// /// assert_eq!(&format!("{:.4}", Foo(23.2)), "Foo(23.2000)"); /// assert_eq!(&format!("{}", Foo(23.2)), "Foo(23.20)"); /// ``` #[stable(feature = "fmt_flags", since = "1.5.0")] pub fn precision(&self) -> Option<usize> { self.precision } /// Determines if the `+` flag was specified. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo(i32); /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// if formatter.sign_plus() { /// write!(formatter, /// "Foo({}{})", /// if self.0 < 0 { '-' } else { '+' }, /// self.0) /// } else { /// write!(formatter, "Foo({})", self.0) /// } /// } /// } /// /// assert_eq!(&format!("{:+}", Foo(23)), "Foo(+23)"); /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)"); /// ``` #[stable(feature = "fmt_flags", since = "1.5.0")] pub fn sign_plus(&self) -> bool { self.flags & (1 << FlagV1::SignPlus as u32) != 0 } /// Determines if the `-` flag was specified. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo(i32); /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// if formatter.sign_minus() { /// // You want a minus sign? Have one! /// write!(formatter, "-Foo({})", self.0) /// } else { /// write!(formatter, "Foo({})", self.0) /// } /// } /// } /// /// assert_eq!(&format!("{:-}", Foo(23)), "-Foo(23)"); /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)"); /// ``` #[stable(feature = "fmt_flags", since = "1.5.0")] pub fn sign_minus(&self) -> bool { self.flags & (1 << FlagV1::SignMinus as u32) != 0 } /// Determines if the `#` flag was specified. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo(i32); /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// if formatter.alternate() { /// write!(formatter, "Foo({})", self.0) /// } else { /// write!(formatter, "{}", self.0) /// } /// } /// } /// /// assert_eq!(&format!("{:#}", Foo(23)), "Foo(23)"); /// assert_eq!(&format!("{}", Foo(23)), "23"); /// ``` #[stable(feature = "fmt_flags", since = "1.5.0")] pub fn alternate(&self) -> bool { self.flags & (1 << FlagV1::Alternate as u32) != 0 } /// Determines if the `0` flag was specified. /// /// # Examples /// /// ``` /// use std::fmt; /// /// struct Foo(i32); /// /// impl fmt::Display for Foo { /// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { /// assert!(formatter.sign_aware_zero_pad()); /// assert_eq!(formatter.width(), Some(4)); /// // We ignore the formatter's options. /// write!(formatter, "{}", self.0) /// } /// } /// /// assert_eq!(&format!("{:04}", Foo(23)), "23"); /// ``` #[stable(feature = "fmt_flags", since = "1.5.0")] pub fn sign_aware_zero_pad(&self) -> bool { self.flags & (1 << FlagV1::SignAwareZeroPad as u32) != 0 } // FIXME: Decide what public API we want for these two flags. // https://github.com/rust-lang/rust/issues/48584 fn debug_lower_hex(&self) -> bool { self.flags & (1 << FlagV1::DebugLowerHex as u32) != 0 } fn debug_upper_hex(&self) -> bool { self.flags & (1 << FlagV1::DebugUpperHex as u32) != 0 } /// Creates a [`DebugStruct`] builder designed to assist with creation of /// [`fmt::Debug`] implementations for structs. /// /// [`DebugStruct`]: ../../std/fmt/struct.DebugStruct.html /// [`fmt::Debug`]: ../../std/fmt/trait.Debug.html /// /// # Examples /// /// ```rust /// use std::fmt; /// use std::net::Ipv4Addr; /// /// struct Foo { /// bar: i32, /// baz: String, /// addr: Ipv4Addr, /// } /// /// impl fmt::Debug for Foo { /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { /// fmt.debug_struct("Foo") /// .field("bar", &self.bar) /// .field("baz", &self.baz) /// .field("addr", &format_args!("{}", self.addr)) /// .finish() /// } /// } /// /// assert_eq!( /// "Foo { bar: 10, baz: \"Hello World\", addr: 127.0.0.1 }", /// format!("{:?}", Foo { /// bar: 10, /// baz: "Hello World".to_string(), /// addr: Ipv4Addr::new(127, 0, 0, 1), /// }) /// ); /// ``` #[stable(feature = "debug_builders", since = "1.2.0")] pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> { builders::debug_struct_new(self, name) } /// Creates a `DebugTuple` builder designed to assist with creation of /// `fmt::Debug` implementations for tuple structs. /// /// # Examples /// /// ```rust /// use std::fmt; /// use std::marker::PhantomData; /// /// struct Foo<T>(i32, String, PhantomData<T>); /// /// impl<T> fmt::Debug for Foo<T> { /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { /// fmt.debug_tuple("Foo") /// .field(&self.0) /// .field(&self.1) /// .field(&format_args!("_")) /// .finish() /// } /// } /// /// assert_eq!( /// "Foo(10, \"Hello\", _)", /// format!("{:?}", Foo(10, "Hello".to_string(), PhantomData::<u8>)) /// ); /// ``` #[stable(feature = "debug_builders", since = "1.2.0")] pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> { builders::debug_tuple_new(self, name) } /// Creates a `DebugList` builder designed to assist with creation of /// `fmt::Debug` implementations for list-like structures. /// /// # Examples /// /// ```rust /// use std::fmt; /// /// struct Foo(Vec<i32>); /// /// impl fmt::Debug for Foo { /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { /// fmt.debug_list().entries(self.0.iter()).finish() /// } /// } /// /// // prints "[10, 11]" /// println!("{:?}", Foo(vec![10, 11])); /// ``` #[stable(feature = "debug_builders", since = "1.2.0")] pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> { builders::debug_list_new(self) } /// Creates a `DebugSet` builder designed to assist with creation of /// `fmt::Debug` implementations for set-like structures. /// /// # Examples /// /// ```rust /// use std::fmt; /// /// struct Foo(Vec<i32>); /// /// impl fmt::Debug for Foo { /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { /// fmt.debug_set().entries(self.0.iter()).finish() /// } /// } /// /// // prints "{10, 11}" /// println!("{:?}", Foo(vec![10, 11])); /// ``` /// /// [`format_args!`]: ../../std/macro.format_args.html /// /// In this more complex example, we use [`format_args!`] and `.debug_set()` /// to build a list of match arms: /// /// ```rust /// use std::fmt; /// /// struct Arm<'a, L: 'a, R: 'a>(&'a (L, R)); /// struct Table<'a, K: 'a, V: 'a>(&'a [(K, V)], V); /// /// impl<'a, L, R> fmt::Debug for Arm<'a, L, R> /// where /// L: 'a + fmt::Debug, R: 'a + fmt::Debug /// { /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { /// L::fmt(&(self.0).0, fmt)?; /// fmt.write_str(" => ")?; /// R::fmt(&(self.0).1, fmt) /// } /// } /// /// impl<'a, K, V> fmt::Debug for Table<'a, K, V> /// where /// K: 'a + fmt::Debug, V: 'a + fmt::Debug /// { /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { /// fmt.debug_set() /// .entries(self.0.iter().map(Arm)) /// .entry(&Arm(&(format_args!("_"), &self.1))) /// .finish() /// } /// } /// ``` #[stable(feature = "debug_builders", since = "1.2.0")] pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> { builders::debug_set_new(self) } /// Creates a `DebugMap` builder designed to assist with creation of /// `fmt::Debug` implementations for map-like structures. /// /// # Examples /// /// ```rust /// use std::fmt; /// /// struct Foo(Vec<(String, i32)>); /// /// impl fmt::Debug for Foo { /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { /// fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish() /// } /// } /// /// // prints "{"A": 10, "B": 11}" /// println!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])); /// ``` #[stable(feature = "debug_builders", since = "1.2.0")] pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> { builders::debug_map_new(self) } } #[stable(since = "1.2.0", feature = "formatter_write")] impl Write for Formatter<'_> { fn write_str(&mut self, s: &str) -> Result { self.buf.write_str(s) } fn write_char(&mut self, c: char) -> Result { self.buf.write_char(c) } fn write_fmt(&mut self, args: Arguments<'_>) -> Result { write(self.buf, args) } } #[stable(feature = "rust1", since = "1.0.0")] impl Display for Error { fn fmt(&self, f: &mut Formatter<'_>) -> Result { Display::fmt("an error occurred when formatting an argument", f) } } // Implementations of the core formatting traits macro_rules! fmt_refs { ($($tr:ident),*) => { $( #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + $tr> $tr for &T { fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + $tr> $tr for &mut T { fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) } } )* } } fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp } #[unstable(feature = "never_type", issue = "35121")] impl Debug for ! { fn fmt(&self, _: &mut Formatter<'_>) -> Result { *self } } #[unstable(feature = "never_type", issue = "35121")] impl Display for ! { fn fmt(&self, _: &mut Formatter<'_>) -> Result { *self } } #[stable(feature = "rust1", since = "1.0.0")] impl Debug for bool { #[inline] fn fmt(&self, f: &mut Formatter<'_>) -> Result { Display::fmt(self, f) } } #[stable(feature = "rust1", since = "1.0.0")] impl Display for bool { fn fmt(&self, f: &mut Formatter<'_>) -> Result { Display::fmt(if *self { "true" } else { "false" }, f) } } #[stable(feature = "rust1", since = "1.0.0")] impl Debug for str { fn fmt(&self, f: &mut Formatter<'_>) -> Result { f.write_char('"')?; let mut from = 0; for (i, c) in self.char_indices() { let esc = c.escape_debug(); // If char needs escaping, flush backlog so far and write, else skip if esc.len() != 1 { f.write_str(&self[from..i])?; for c in esc { f.write_char(c)?; } from = i + c.len_utf8(); } } f.write_str(&self[from..])?; f.write_char('"') } } #[stable(feature = "rust1", since = "1.0.0")] impl Display for str { fn fmt(&self, f: &mut Formatter<'_>) -> Result { f.pad(self) } } #[stable(feature = "rust1", since = "1.0.0")] impl Debug for char { fn fmt(&self, f: &mut Formatter<'_>) -> Result { f.write_char('\'')?; for c in self.escape_debug() { f.write_char(c)? } f.write_char('\'') } } #[stable(feature = "rust1", since = "1.0.0")] impl Display for char { fn fmt(&self, f: &mut Formatter<'_>) -> Result { if f.width.is_none() && f.precision.is_none() { f.write_char(*self) } else { f.pad(self.encode_utf8(&mut [0; 4])) } } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> Pointer for *const T { fn fmt(&self, f: &mut Formatter<'_>) -> Result { let old_width = f.width; let old_flags = f.flags; // The alternate flag is already treated by LowerHex as being special- // it denotes whether to prefix with 0x. We use it to work out whether // or not to zero extend, and then unconditionally set it to get the // prefix. if f.alternate() { f.flags |= 1 << (FlagV1::SignAwareZeroPad as u32); if let None = f.width { f.width = Some(((mem::size_of::<usize>() * 8) / 4) + 2); } } f.flags |= 1 << (FlagV1::Alternate as u32); let ret = LowerHex::fmt(&(*self as *const () as usize), f); f.width = old_width; f.flags = old_flags; ret } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> Pointer for *mut T { fn fmt(&self, f: &mut Formatter<'_>) -> Result { Pointer::fmt(&(*self as *const T), f) } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> Pointer for &T { fn fmt(&self, f: &mut Formatter<'_>) -> Result { Pointer::fmt(&(*self as *const T), f) } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> Pointer for &mut T { fn fmt(&self, f: &mut Formatter<'_>) -> Result { Pointer::fmt(&(&**self as *const T), f) } } // Implementation of Display/Debug for various core types #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> Debug for *const T { fn fmt(&self, f: &mut Formatter<'_>) -> Result { Pointer::fmt(self, f) } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> Debug for *mut T { fn fmt(&self, f: &mut Formatter<'_>) -> Result { Pointer::fmt(self, f) } } macro_rules! peel { ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* }) } macro_rules! tuple { () => (); ( $($name:ident,)+ ) => ( #[stable(feature = "rust1", since = "1.0.0")] impl<$($name:Debug),*> Debug for ($($name,)*) where last_type!($($name,)+): ?Sized { #[allow(non_snake_case, unused_assignments)] fn fmt(&self, f: &mut Formatter<'_>) -> Result { let mut builder = f.debug_tuple(""); let ($(ref $name,)*) = *self; $( builder.field(&$name); )* builder.finish() } } peel! { $($name,)* } ) } macro_rules! last_type { ($a:ident,) => { $a }; ($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) }; } tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, } #[stable(feature = "rust1", since = "1.0.0")] impl<T: Debug> Debug for [T] { fn fmt(&self, f: &mut Formatter<'_>) -> Result { f.debug_list().entries(self.iter()).finish() } } #[stable(feature = "rust1", since = "1.0.0")] impl Debug for () { #[inline] fn fmt(&self, f: &mut Formatter<'_>) -> Result { f.pad("()") } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> Debug for PhantomData<T> { fn fmt(&self, f: &mut Formatter<'_>) -> Result { f.pad("PhantomData") } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: Copy + Debug> Debug for Cell<T> { fn fmt(&self, f: &mut Formatter<'_>) -> Result { f.debug_struct("Cell") .field("value", &self.get()) .finish() } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + Debug> Debug for RefCell<T> { fn fmt(&self, f: &mut Formatter<'_>) -> Result { match self.try_borrow() { Ok(borrow) => { f.debug_struct("RefCell") .field("value", &borrow) .finish() } Err(_) => { // The RefCell is mutably borrowed so we can't look at its value // here. Show a placeholder instead. struct BorrowedPlaceholder; impl Debug for BorrowedPlaceholder { fn fmt(&self, f: &mut Formatter<'_>) -> Result { f.write_str("<borrowed>") } } f.debug_struct("RefCell") .field("value", &BorrowedPlaceholder) .finish() } } } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + Debug> Debug for Ref<'_, T> { fn fmt(&self, f: &mut Formatter<'_>) -> Result { Debug::fmt(&**self, f) } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + Debug> Debug for RefMut<'_, T> { fn fmt(&self, f: &mut Formatter<'_>) -> Result { Debug::fmt(&*(self.deref()), f) } } #[stable(feature = "core_impl_debug", since = "1.9.0")] impl<T: ?Sized + Debug> Debug for UnsafeCell<T> { fn fmt(&self, f: &mut Formatter<'_>) -> Result { f.pad("UnsafeCell") } } // If you expected tests to be here, look instead at the run-pass/ifmt.rs test, // it's a lot easier than creating all of the rt::Piece structures here.