DebugList in core::fmt - Rust (original) (raw)

Struct DebugList

1.6.0 · Source

pub struct DebugList<'a, 'b: 'a> { /* private fields */ }

Expand description

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]",
);

Source§

1.2.0 · Source

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]]",
);

Source

🔬This is a nightly-only experimental API. (debug_closure_helpers #117729)

Adds a new entry to the list output.

This method is equivalent to DebugList::entry, but formats the entry using a provided closure rather than by calling Debug::fmt.

1.2.0 · Source

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]",
);

1.83.0 · Source

Marks the list as non-exhaustive, indicating to the reader that there are some other elements that are not shown in the debug representation.

§Examples

use std::fmt;

struct Foo(Vec<i32>);

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Print at most two elements, abbreviate the rest
        let mut f = fmt.debug_list();
        let mut f = f.entries(self.0.iter().take(2));
        if self.0.len() > 2 {
            f.finish_non_exhaustive()
        } else {
            f.finish()
        }
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![1, 2, 3, 4])),
    "[1, 2, ..]",
);

1.2.0 · Source

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 list formatting.
    }
}

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

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