# 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]",
    );

## Implementations§

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### impl<'a, 'b: 'a> DebugList<'a, 'b>

1.2.0 · Source

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

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]]",
    );

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#### 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 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

#### 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 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

#### pub fn finish_non_exhaustive(&mut self) -> Result

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

#### 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_list()
               .entries(self.0.iter())
               .finish() // Ends the list formatting.
        }
    }

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

## Auto Trait Implementations§

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### impl<'a, 'b> Freeze for DebugList<'a, 'b>

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### impl<'a, 'b> !RefUnwindSafe for DebugList<'a, 'b>

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### impl<'a, 'b> !Send for DebugList<'a, 'b>

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### impl<'a, 'b> !Sync for DebugList<'a, 'b>

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### impl<'a, 'b> Unpin for DebugList<'a, 'b>

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### impl<'a, 'b> !UnwindSafe for DebugList<'a, 'b>

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.