Struct DebugStruct

#[must_use = "must eventually call `finish()` on Debug builders"]
pub struct DebugStruct<'a, 'b: 'a> { pub(in ::fmt::builders) fmt: &'a mut Formatter<'b>, pub(in ::fmt::builders) result: Result, pub(in ::fmt::builders) has_fields: bool }

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" }"#,
);

Fields

fmt: &'a mut Formatter<'b>
result: Result
has_fields: bool

Implementations

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

fn field(&mut self, name: &str, value: &dyn Debug) -> &mut Self

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 }"#,
);

fn field_with<F>(&mut self, name: &str, value_fmt: F) -> &mut Self
where
    F: FnOnce(&mut Formatter<'_>) -> Result,

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.

fn finish_non_exhaustive(&mut self) -> Result

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, .. }",
);

fn finish(&mut self) -> Result

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" }"#,
);

fn is_pretty(&self) -> bool

Auto Trait Implementations

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

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

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

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

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

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

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

Blanket Implementations

impl<T> Any for DebugStruct<'a, 'b> where T: 'static + ?Sized,

fn type_id(&self) -> TypeId

impl<T> Borrow<T> for DebugStruct<'a, 'b> where T: ?Sized,

fn borrow(&self) -> &T

impl<T> BorrowMut<T> for DebugStruct<'a, 'b> where T: ?Sized,

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

impl<T> From<T> for DebugStruct<'a, 'b>

fn from(t: T) -> T

Returns the argument unchanged.

impl<T> SizeHint for DebugStruct<'a, 'b> where T: ?Sized,

fn lower_bound(&self) -> usize
fn upper_bound(&self) -> Option<usize>

impl<T> SizedTypeProperties for DebugStruct<'a, 'b>

impl<T, U> Into<U> for DebugStruct<'a, 'b> where U: From<T>,

fn into(self) -> U

Calls U::from(self).

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

impl<T, U> TryFrom<U> for DebugStruct<'a, 'b> where U: Into<T>,

type Error = Infallible;
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

impl<T, U> TryInto<U> for DebugStruct<'a, 'b> where U: TryFrom<T>,

type Error = <U as TryFrom<T>>::Error;
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>