Struct core::fmt::DebugSet

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

A struct to help with fmt::Debug implementations.

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

This can be constructed by the Formatter::debug_set 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_set().entries(self.0.iter()).finish()
    }
}

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

Implementations

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

pub fn entry(&mut self, entry: &dyn Debug) -> &mut Self

Adds a new entry to the set 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_set()
           .entry(&self.0) // Adds the first "entry".
           .entry(&self.1) // Adds the second "entry".
           .finish()
    }
}

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

pub fn entry_with<F>(&mut self, entry_fmt: F) -> &mut Self

where F: FnOnce(&mut Formatter<'_>) -> Result,

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

Adds a new entry to the set output.

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

pub fn entries<D, I>(&mut self, entries: I) -> &mut Self

where D: Debug, I: IntoIterator<Item = D>,

Adds the contents of an iterator of entries to the set 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_set()
           .entries(self.0.iter()) // Adds the first "entry".
           .entries(self.1.iter()) // Adds the second "entry".
           .finish()
    }
}

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

pub fn finish_non_exhaustive(&mut self) -> Result

🔬This is a nightly-only experimental API. (debug_more_non_exhaustive #127942)

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

Examples

#![feature(debug_more_non_exhaustive)]

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_set();
        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, ..}",
);

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_set()
           .entries(self.0.iter())
           .finish() // Ends the set formatting.
    }
}

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