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.
Similar to Option
and Result
, this enum can be used with the ?
operator
to return immediately if the Break
variant is present or otherwise continue normally
with the value inside the Continue
variant.
§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));
A 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, f: &mut impl FnMut(&T) -> ControlFlow<B>) -> ControlFlow<B> {
if let Some(left) = &self.left {
left.traverse_inorder(f)?;
}
f(&self.value)?;
if let Some(right) = &self.right {
right.traverse_inorder(f)?;
}
ControlFlow::Continue(())
}
fn leaf(value: T) -> Option<Box<TreeNode<T>>> {
Some(Box::new(Self { value, left: None, right: None }))
}
}
let node = TreeNode {
value: 0,
left: TreeNode::leaf(1),
right: Some(Box::new(TreeNode {
value: -1,
left: TreeNode::leaf(5),
right: TreeNode::leaf(2),
}))
};
let mut sum = 0;
let res = node.traverse_inorder(&mut |val| {
if *val < 0 {
ControlFlow::Break(*val)
} else {
sum += *val;
ControlFlow::Continue(())
}
});
assert_eq!(res, ControlFlow::Break(-1));
assert_eq!(sum, 6);
Variants§
Continue(C)
Move on to the next phase of the operation as normal.
Break(B)
Exit the operation without running subsequent phases.
Implementations§
source§impl<B, C> ControlFlow<B, C>
impl<B, C> ControlFlow<B, C>
1.59.0 · sourcepub fn is_break(&self) -> bool
pub fn is_break(&self) -> bool
Returns true
if this is a Break
variant.
§Examples
use std::ops::ControlFlow;
assert!(ControlFlow::<i32, String>::Break(3).is_break());
assert!(!ControlFlow::<String, i32>::Continue(3).is_break());
1.59.0 · sourcepub fn is_continue(&self) -> bool
pub fn is_continue(&self) -> bool
Returns true
if this is a Continue
variant.
§Examples
use std::ops::ControlFlow;
assert!(!ControlFlow::<i32, String>::Break(3).is_continue());
assert!(ControlFlow::<String, i32>::Continue(3).is_continue());
1.83.0 · sourcepub fn break_value(self) -> Option<B>
pub fn break_value(self) -> Option<B>
Converts the ControlFlow
into an Option
which is Some
if the
ControlFlow
was Break
and None
otherwise.
§Examples
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);
1.83.0 · sourcepub fn map_break<T>(self, f: impl FnOnce(B) -> T) -> ControlFlow<T, C>
pub fn map_break<T>(self, f: impl FnOnce(B) -> T) -> ControlFlow<T, C>
Maps ControlFlow<B, C>
to ControlFlow<T, C>
by applying a function
to the break value in case it exists.
1.83.0 · sourcepub fn continue_value(self) -> Option<C>
pub fn continue_value(self) -> Option<C>
Converts the ControlFlow
into an Option
which is Some
if the
ControlFlow
was Continue
and None
otherwise.
§Examples
use std::ops::ControlFlow;
assert_eq!(ControlFlow::<i32, String>::Break(3).continue_value(), None);
assert_eq!(ControlFlow::<String, i32>::Continue(3).continue_value(), Some(3));
1.83.0 · sourcepub fn map_continue<T>(self, f: impl FnOnce(C) -> T) -> ControlFlow<B, T>
pub fn map_continue<T>(self, f: impl FnOnce(C) -> T) -> ControlFlow<B, T>
Maps ControlFlow<B, C>
to ControlFlow<B, T>
by applying a function
to the continue value in case it exists.
impl<R> ControlFlow<R, <R as Try>::Output>where
R: Try,
These are used only as part of implementing the iterator adapters. They have mediocre names and non-obvious semantics, so aren’t currently on a path to potential stabilization.
Trait Implementations§
1.55.0 · source§impl<B, C> Clone for ControlFlow<B, C>
impl<B, C> Clone for ControlFlow<B, C>
source§fn clone(&self) -> ControlFlow<B, C>
fn clone(&self) -> ControlFlow<B, C>
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read more1.55.0 · source§impl<B, C> Debug for ControlFlow<B, C>
impl<B, C> Debug for ControlFlow<B, C>
source§impl<B, C> FromResidual<ControlFlow<B, Infallible>> for ControlFlow<B, C>
impl<B, C> FromResidual<ControlFlow<B, Infallible>> for ControlFlow<B, C>
source§fn from_residual(residual: ControlFlow<B, Infallible>) -> ControlFlow<B, C>
fn from_residual(residual: ControlFlow<B, Infallible>) -> ControlFlow<B, C>
try_trait_v2
)Residual
type. Read more1.55.0 · source§impl<B, C> Hash for ControlFlow<B, C>
impl<B, C> Hash for ControlFlow<B, C>
1.55.0 · source§impl<B, C> PartialEq for ControlFlow<B, C>
impl<B, C> PartialEq for ControlFlow<B, C>
source§impl<B, C> Residual<C> for ControlFlow<B, Infallible>
impl<B, C> Residual<C> for ControlFlow<B, Infallible>
source§type TryType = ControlFlow<B, C>
type TryType = ControlFlow<B, C>
try_trait_v2_residual
)source§impl<B, C> Try for ControlFlow<B, C>
impl<B, C> Try for ControlFlow<B, C>
source§type Output = C
type Output = C
try_trait_v2
)?
when not short-circuiting.source§type Residual = ControlFlow<B, Infallible>
type Residual = ControlFlow<B, Infallible>
try_trait_v2
)FromResidual::from_residual
as part of ?
when short-circuiting. Read moresource§fn from_output(output: <ControlFlow<B, C> as Try>::Output) -> ControlFlow<B, C>
fn from_output(output: <ControlFlow<B, C> as Try>::Output) -> ControlFlow<B, C>
try_trait_v2
)Output
type. Read moresource§fn branch(
self,
) -> ControlFlow<<ControlFlow<B, C> as Try>::Residual, <ControlFlow<B, C> as Try>::Output>
fn branch( self, ) -> ControlFlow<<ControlFlow<B, C> as Try>::Residual, <ControlFlow<B, C> as Try>::Output>
try_trait_v2
)?
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 moreimpl<B, C> Copy for ControlFlow<B, C>
impl<B, C> Eq for ControlFlow<B, C>
impl<B, C> StructuralPartialEq for ControlFlow<B, C>
Auto Trait Implementations§
impl<B, C> Freeze for ControlFlow<B, C>
impl<B, C> RefUnwindSafe for ControlFlow<B, C>where
C: RefUnwindSafe,
B: RefUnwindSafe,
impl<B, C> Send for ControlFlow<B, C>
impl<B, C> Sync for ControlFlow<B, C>
impl<B, C> Unpin for ControlFlow<B, C>
impl<B, C> UnwindSafe for ControlFlow<B, C>where
C: UnwindSafe,
B: UnwindSafe,
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T> CloneToUninit for Twhere
T: Clone,
impl<T> CloneToUninit for Twhere
T: Clone,
source§unsafe fn clone_to_uninit(&self, dst: *mut T)
unsafe fn clone_to_uninit(&self, dst: *mut T)
clone_to_uninit
)§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
§fn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
§fn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
key
and return true
if they are equal.