[−][src]Function replace_with::replace_with
pub fn replace_with<T, D: FnOnce() -> T, F: FnOnce(T) -> T>(
dest: &mut T,
default: D,
f: F
)
Temporarily takes ownership of a value at a mutable location, and replace it with a new value based on the old one.
We move out of the reference temporarily, to apply a closure f
, returning a new value, which
is then placed at the original value's location.
An important note
On panic (or to be more precise, unwinding) of the closure f
, default
will be called to
provide a replacement value. default
should not panic – doing so will constitute a double
panic and will most likely abort the process.
Example
enum States { A(String), B(String), } impl States { fn poll(&mut self) { replace_with( self, || States::A(String::new()), |self_| match self_ { States::A(a) => States::B(a), States::B(a) => States::A(a), }, ); } }