Struct tracing::stdlib::fmt::DebugTuple

pub struct DebugTuple<'a, 'b>
where
    'b: 'a,
{
    fmt: &'a mut Formatter<'b>,
    result: Result<(), Error>,
    fields: usize,
    empty_name: bool,
}

A struct to help with fmt::Debug implementations.

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

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

Examples

use std::fmt;

struct Foo(i32, String);

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

assert_eq!(
    format!("{:?}", Foo(10, "Hello World".to_string())),
    r#"Foo(10, "Hello World")"#,
);

Fields

fmt: &'a mut Formatter<'b>

result: Result<(), Error>

fields: usize

empty_name: bool

Implementations

impl<'a, 'b> DebugTuple<'a, 'b>

where 'b: 'a,

pub fn field(&mut self, value: &dyn Debug) -> &mut DebugTuple<'a, 'b>

Adds a new field to the generated tuple struct output.

Examples

use std::fmt;

struct Foo(i32, String);

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.debug_tuple("Foo")
           .field(&self.0) // We add the first field.
           .field(&self.1) // We add the second field.
           .finish() // We're good to go!
    }
}

assert_eq!(
    format!("{:?}", Foo(10, "Hello World".to_string())),
    r#"Foo(10, "Hello World")"#,
);

pub fn field_with<F>(&mut self, value_fmt: F) -> &mut DebugTuple<'a, 'b>

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

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

Adds a new field to the generated tuple struct output.

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

pub fn finish_non_exhaustive(&mut self) -> Result<(), Error>

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

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

Examples

#![feature(debug_more_non_exhaustive)]

use std::fmt;

struct Foo(i32, String);

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.debug_tuple("Foo")
           .field(&self.0)
           .finish_non_exhaustive() // Show that some other field(s) exist.
    }
}

assert_eq!(
    format!("{:?}", Foo(10, "secret!".to_owned())),
    "Foo(10, ..)",
);

pub fn finish(&mut self) -> Result<(), Error>

Finishes output and returns any error encountered.

Examples

use std::fmt;

struct Foo(i32, String);

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.debug_tuple("Foo")
           .field(&self.0)
           .field(&self.1)
           .finish() // You need to call it to "finish" the
                     // tuple formatting.
    }
}

assert_eq!(
    format!("{:?}", Foo(10, "Hello World".to_string())),
    r#"Foo(10, "Hello World")"#,
);