Enum std::ops::ControlFlow 1.55.0[−][src]
pub enum ControlFlow<B, C = ()> {
Continue(C),
Break(B),
}
Expand description
Used to tell an operation whether it should exit early or go on as usual.
This is used when exposing things (like graph traversals or visitors) where
you want the user to be able to choose whether to exit early.
Having the enum makes it clearer – no more wondering “wait, what did false
mean again?” – and allows including a value.
Examples
Early-exiting from Iterator::try_for_each
:
use std::ops::ControlFlow;
let r = (2..100).try_for_each(|x| {
if 403 % x == 0 {
return ControlFlow::Break(x)
}
ControlFlow::Continue(())
});
assert_eq!(r, ControlFlow::Break(13));
RunA basic tree traversal:
use std::ops::ControlFlow;
pub struct TreeNode<T> {
value: T,
left: Option<Box<TreeNode<T>>>,
right: Option<Box<TreeNode<T>>>,
}
impl<T> TreeNode<T> {
pub fn traverse_inorder<B>(&self, mut f: impl FnMut(&T) -> ControlFlow<B>) -> ControlFlow<B> {
if let Some(left) = &self.left {
left.traverse_inorder(&mut f)?;
}
f(&self.value)?;
if let Some(right) = &self.right {
right.traverse_inorder(&mut f)?;
}
ControlFlow::Continue(())
}
}
RunVariants
Move on to the next phase of the operation as normal.
Exit the operation without running subsequent phases.
Implementations
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
Converts the ControlFlow
into an Option
which is Some
if the
ControlFlow
was Break
and None
otherwise.
Examples
#![feature(control_flow_enum)]
use std::ops::ControlFlow;
assert_eq!(ControlFlow::<i32, String>::Break(3).break_value(), Some(3));
assert_eq!(ControlFlow::<String, i32>::Continue(3).break_value(), None);
Run🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
Maps ControlFlow<B, C>
to ControlFlow<T, C>
by applying a function
to the break value in case it exists.
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
It’s frequently the case that there’s no value needed with Continue
,
so this provides a way to avoid typing (())
, if you prefer it.
Examples
#![feature(control_flow_enum)]
use std::ops::ControlFlow;
let mut partial_sum = 0;
let last_used = (1..10).chain(20..25).try_for_each(|x| {
partial_sum += x;
if partial_sum > 100 { ControlFlow::Break(x) }
else { ControlFlow::CONTINUE }
});
assert_eq!(last_used.break_value(), Some(22));
Run🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
🔬 This is a nightly-only experimental API. (control_flow_enum
#75744)
new API
APIs like try_for_each
don’t need values with Break
,
so this provides a way to avoid typing (())
, if you prefer it.
Examples
#![feature(control_flow_enum)]
use std::ops::ControlFlow;
let mut partial_sum = 0;
(1..10).chain(20..25).try_for_each(|x| {
if partial_sum > 100 { ControlFlow::BREAK }
else { partial_sum += x; ControlFlow::CONTINUE }
});
assert_eq!(partial_sum, 108);
RunTrait Implementations
impl<B, C> PartialEq<ControlFlow<B, C>> for ControlFlow<B, C> where
B: PartialEq<B>,
C: PartialEq<C>,
impl<B, C> PartialEq<ControlFlow<B, C>> for ControlFlow<B, C> where
B: PartialEq<B>,
C: PartialEq<C>,
This method tests for self
and other
values to be equal, and is used
by ==
. Read more
This method tests for !=
.
type Residual = ControlFlow<B, Infallible>
type Residual = ControlFlow<B, Infallible>
The type of the value passed to FromResidual::from_residual
as part of ?
when short-circuiting. Read more
pub fn branch(
self
) -> ControlFlow<<ControlFlow<B, C> as Try>::Residual, <ControlFlow<B, C> as Try>::Output>
pub fn branch(
self
) -> ControlFlow<<ControlFlow<B, C> as Try>::Residual, <ControlFlow<B, C> as Try>::Output>
Used in ?
to decide whether the operator should produce a value
(because this returned ControlFlow::Continue
)
or propagate a value back to the caller
(because this returned ControlFlow::Break
). Read more
Auto Trait Implementations
impl<B, C> RefUnwindSafe for ControlFlow<B, C> where
B: RefUnwindSafe,
C: RefUnwindSafe,
impl<B, C> Send for ControlFlow<B, C> where
B: Send,
C: Send,
impl<B, C> Sync for ControlFlow<B, C> where
B: Sync,
C: Sync,
impl<B, C> Unpin for ControlFlow<B, C> where
B: Unpin,
C: Unpin,
impl<B, C> UnwindSafe for ControlFlow<B, C> where
B: UnwindSafe,
C: UnwindSafe,
Blanket Implementations
Mutably borrows from an owned value. Read more