ControlFlow in std::ops - Rust (original) (raw)
Enum ControlFlow
1.55.0 · Source
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 falsemean 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);§1.55.0
Move on to the next phase of the operation as normal.
§1.55.0
Exit the operation without running subsequent phases.
1.59.0 · Source
Returns true if this is a Break variant.
§Examples
use std::ops::ControlFlow;
assert!(ControlFlow::<&str, i32>::Break("Stop right there!").is_break());
assert!(!ControlFlow::<&str, i32>::Continue(3).is_break());1.59.0 · Source
Returns true if this is a Continue variant.
§Examples
use std::ops::ControlFlow;
assert!(!ControlFlow::<&str, i32>::Break("Stop right there!").is_continue());
assert!(ControlFlow::<&str, i32>::Continue(3).is_continue());1.83.0 · Source
Converts the ControlFlow into an Option which is Some if theControlFlow was Break and None otherwise.
§Examples
use std::ops::ControlFlow;
assert_eq!(ControlFlow::<&str, i32>::Break("Stop right there!").break_value(), Some("Stop right there!"));
assert_eq!(ControlFlow::<&str, i32>::Continue(3).break_value(), None);1.83.0 · Source
Maps ControlFlow<B, C> to ControlFlow<T, C> by applying a function to the break value in case it exists.
1.83.0 · Source
Converts the ControlFlow into an Option which is Some if theControlFlow was Continue and None otherwise.
§Examples
use std::ops::ControlFlow;
assert_eq!(ControlFlow::<&str, i32>::Break("Stop right there!").continue_value(), None);
assert_eq!(ControlFlow::<&str, i32>::Continue(3).continue_value(), Some(3));1.83.0 · Source
Maps ControlFlow<B, C> to ControlFlow<B, T> by applying a function to the continue value in case it exists.
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.
This impl block contains no items.
🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
Constructs the type from a compatible Residual type. Read more
Tests for self and other values to be equal, and is used by ==.
Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
🔬This is a nightly-only experimental API. (try_trait_v2_residual #91285)
The “return” type of this meta-function.
🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
The type of the value produced by ? when not short-circuiting.
🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
Constructs the type from its Output type. Read more
🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
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