DebugStruct in alloc::fmt - Rust
Description: A struct to help with `fmt::Debug` implementations.

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## DebugStruct

# Struct DebugStruct

1.36.0 · Source

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

Expand description

A struct to help with `fmt::Debug` implementations.

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

This can be constructed by the `Formatter::debug_struct` method.

## §Examples

    use std::fmt;

    struct Foo {
        bar: i32,
        baz: String,
    }

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

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

## Implementations§

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### impl<'a, 'b> DebugStruct<'a, 'b>
where 'b: 'a,

1.2.0 · Source

#### pub fn field( &mut self, name: &str, value: &dyn Debug, ) -> &mut DebugStruct<'a, 'b>

Adds a new field to the generated struct output.

##### §Examples

    use std::fmt;

    struct Bar {
        bar: i32,
        another: String,
    }

    impl fmt::Debug for Bar {
        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt.debug_struct("Bar")
               .field("bar", &self.bar) // We add `bar` field.
               .field("another", &self.another) // We add `another` field.
               // We even add a field which doesn't exist (because why not?).
               .field("nonexistent_field", &1)
               .finish() // We're good to go!
        }
    }

    assert_eq!(
        format!("{:?}", Bar { bar: 10, another: "Hello World".to_string() }),
        r#"Bar { bar: 10, another: "Hello World", nonexistent_field: 1 }"#,
    );

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#### pub fn field_with<F>( &mut self, name: &str, value_fmt: F, ) -> &mut DebugStruct<'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 struct output.

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

1.53.0 · Source

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

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

##### §Examples

    use std::fmt;

    struct Bar {
        bar: i32,
        hidden: f32,
    }

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

    assert_eq!(
        format!("{:?}", Bar { bar: 10, hidden: 1.0 }),
        "Bar { bar: 10, .. }",
    );

1.2.0 · Source

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

Finishes output and returns any error encountered.

##### §Examples

    use std::fmt;

    struct Bar {
        bar: i32,
        baz: String,
    }

    impl fmt::Debug for Bar {
        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt.debug_struct("Bar")
               .field("bar", &self.bar)
               .field("baz", &self.baz)
               .finish() // You need to call it to "finish" the
                         // struct formatting.
        }
    }

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

## Auto Trait Implementations§

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

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

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

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

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

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### impl<'a, 'b> UnsafeUnpin for DebugStruct<'a, 'b>

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### impl<'a, 'b> !UnwindSafe for DebugStruct<'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.