Struct DebugOnce 

struct DebugOnce<F>(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.

Tuple 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

Formats the value using the given formatter.