1.2.0[][src]Struct std::fmt::DebugMap

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

A struct to help with fmt::Debug implementations.

This is useful when you wish to output a formatted map as a part of your Debug::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)])),
    "{\"A\": 10, \"B\": 11}",
);Run

Methods

impl<'a, 'b> DebugMap<'a, 'b> where
    'b: 'a, 
[src]

pub fn entry(
    &mut self,
    key: &dyn Debug,
    value: &dyn Debug
) -> &mut DebugMap<'a, 'b>
[src]

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)])),
    "{\"whole\": [(\"A\", 10), (\"B\", 11)]}",
);Run

pub fn key(&mut self, key: &dyn Debug) -> &mut DebugMap<'a, 'b>[src]

🔬 This is a nightly-only experimental API. (debug_map_key_value #62482)

recently added

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 entry method 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)])),
    "{\"whole\": [(\"A\", 10), (\"B\", 11)]}",
);Run

pub fn value(&mut self, value: &dyn Debug) -> &mut DebugMap<'a, 'b>[src]

🔬 This is a nightly-only experimental API. (debug_map_key_value #62482)

recently added

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 entry method 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)])),
    "{\"whole\": [(\"A\", 10), (\"B\", 11)]}",
);Run

pub fn entries<K, V, I>(&mut self, entries: I) -> &mut DebugMap<'a, 'b> where
    I: IntoIterator<Item = (K, V)>,
    K: Debug,
    V: Debug
[src]

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)])),
    "{\"A\": 10, \"B\": 11}",
);Run

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

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 struct formatting.
    }
}

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

Auto Trait Implementations

impl<'a, 'b> !UnwindSafe for DebugMap<'a, 'b>

impl<'a, 'b> !RefUnwindSafe for DebugMap<'a, 'b>

impl<'a, 'b> Unpin for DebugMap<'a, 'b> where
    'b: 'a, 

impl<'a, 'b> !Sync for DebugMap<'a, 'b>

impl<'a, 'b> !Send for DebugMap<'a, 'b>

Blanket Implementations

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> From<T> for T[src]

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> Any for T where
    T: 'static + ?Sized
[src]