Struct DebugOnce
pub(in ::fmt::builders) struct DebugOnce<F>(pub(in ::fmt::builders) Cell<Option<F>>);Wraps an FnOnce formatting closure in a type that implements fmt::Debug by calling the
closure, allowing the *_with builder methods to forward to their &dyn fmt::Debug
counterparts.
By doing this, the builder logic is monomorphized only once and not for every closure type (see #149745).
Formatting a DebugOnce consumes the closure, so attempting to format it more than once
panics. This never happens because the debug builders format each value exactly once.
Fields
0: Cell<Option<F>>
Trait Implementations
impl<F> Debug for DebugOnce<F>
where
F: FnOnce(&mut Formatter<'_>) -> Result,
fn fmt(&self, f: &mut Formatter<'_>) -> Result
Auto Trait Implementations
impl<F> !Freeze for DebugOnce<F>
impl<F> !RefUnwindSafe for DebugOnce<F>
impl<F> !Sync for DebugOnce<F>
impl<F> Send for DebugOnce<F>
where
Cell<Option<F>>: Send,
impl<F> Unpin for DebugOnce<F>
where
Cell<Option<F>>: Unpin,
impl<F> UnsafeUnpin for DebugOnce<F>
where
Cell<Option<F>>: UnsafeUnpin,
impl<F> UnwindSafe for DebugOnce<F>
where
Cell<Option<F>>: UnwindSafe,
Blanket Implementations
impl<T> Any for DebugOnce<F>
where
T: 'static + ?Sized,
fn type_id(&self) -> TypeId
impl<T> Borrow<T> for DebugOnce<F>
where
T: ?Sized,
fn borrow(&self) -> &T
impl<T> BorrowMut<T> for DebugOnce<F>
where
T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
impl<T> From<T> for DebugOnce<F>
fn from(t: T) -> TReturns the argument unchanged.
impl<T> SizeHint for DebugOnce<F>
where
T: ?Sized,
fn lower_bound(&self) -> usizefn upper_bound(&self) -> Option<usize>
impl<T> SizedTypeProperties for DebugOnce<F>
impl<T, U> Into<U> for DebugOnce<F>
where
U: From<T>,
fn into(self) -> UCalls
U::from(self).That is, this conversion is whatever the implementation of
[From]<T> for Uchooses to do.
impl<T, U> TryFrom<U> for DebugOnce<F>
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 DebugOnce<F>
where
U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error;fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>