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

Struct DebugMap

1.6.0 · Source

pub struct DebugMap<'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 map as a part of yourDebug::fmt implementation.

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

§Examples

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()
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
    r#"{"A": 10, "B": 11}"#,
);

Source§

1.2.0 · Source

Adds a new entry to the map output.

§Examples

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()
           .entry(&"whole", &self.0) // We add the "whole" entry.
           .finish()
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
    r#"{"whole": [("A", 10), ("B", 11)]}"#,
);

1.42.0 · Source

Adds the key part of a new entry to the map output.

This method, together with value, is an alternative to entry that can be used when the complete entry isn’t known upfront. Prefer the entrymethod when it’s possible to use.

§Panics

key must be called before value and each call to key must be followed by a corresponding call to value. Otherwise this method will panic.

§Examples

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()
           .key(&"whole").value(&self.0) // We add the "whole" entry.
           .finish()
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
    r#"{"whole": [("A", 10), ("B", 11)]}"#,
);

Source

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

Adds the key part of a new entry to the map output.

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

1.42.0 · Source

Adds the value part of a new entry to the map output.

This method, together with key, is an alternative to entry that can be used when the complete entry isn’t known upfront. Prefer the entrymethod when it’s possible to use.

§Panics

key must be called before value and each call to key must be followed by a corresponding call to value. Otherwise this method will panic.

§Examples

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()
           .key(&"whole").value(&self.0) // We add the "whole" entry.
           .finish()
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
    r#"{"whole": [("A", 10), ("B", 11)]}"#,
);

Source

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

Adds the value part of a new entry to the map output.

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

1.2.0 · Source

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

§Examples

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()
           // We map our vec so each entries' first field will become
           // the "key".
           .entries(self.0.iter().map(|&(ref k, ref v)| (k, v)))
           .finish()
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
    r#"{"A": 10, "B": 11}"#,
);

1.83.0 · Source

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

§Examples

use std::fmt;

struct Foo(Vec<(String, 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_map();
        let mut f = f.entries(self.0.iter().take(2).map(|&(ref k, ref v)| (k, v)));
        if self.0.len() > 2 {
            f.finish_non_exhaustive()
        } else {
            f.finish()
        }
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![
        ("A".to_string(), 10),
        ("B".to_string(), 11),
        ("C".to_string(), 12),
    ])),
    r#"{"A": 10, "B": 11, ..}"#,
);

1.2.0 · Source

Finishes output and returns any error encountered.

§Panics

key must be called before value and each call to key must be followed by a corresponding call to value. Otherwise this method will panic.

§Examples

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() // Ends the map formatting.
    }
}

assert_eq!(
    format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
    r#"{"A": 10, "B": 11}"#,
);

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