Struct core::fmt::DebugList

#[must_use = "must eventually call `finish()` on Debug builders"]
pub struct DebugList<'a, 'b: 'a> { /* fields omitted */ }

A struct to help with fmt::Debug implementations.

This is useful when you wish to output a formatted list of items as a part of your Debug::fmt implementation.

This can be constructed by the Formatter::debug_list method.

Examples

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()
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![10, 11])),
    "[10, 11]",
);

Methods

impl<'a, 'b: 'a> DebugList<'a, 'b>

pub fn entry(&mut self, entry: &dyn Debug) -> &mut DebugList<'a, 'b>

Adds a new entry to the list output.

Examples

use std::fmt;

struct Foo(Vec<i32>, Vec<u32>);

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.debug_list()
           .entry(&self.0) // We add the first "entry".
           .entry(&self.1) // We add the second "entry".
           .finish()
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![10, 11], vec![12, 13])),
    "[[10, 11], [12, 13]]",
);

pub fn entries<D, I>(&mut self, entries: I) -> &mut DebugList<'a, 'b> where
    D: Debug,
    I: IntoIterator<Item = D>, 

Adds the contents of an iterator of entries to the list output.

Examples

use std::fmt;

struct Foo(Vec<i32>, Vec<u32>);

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.debug_list()
           .entries(self.0.iter())
           .entries(self.1.iter())
           .finish()
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![10, 11], vec![12, 13])),
    "[10, 11, 12, 13]",
);

pub fn finish(&mut self) -> Result

Finishes output and returns any error encountered.

Examples

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() // Ends the struct formatting.
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![10, 11])),
    "[10, 11]",
);