Enum std::ops::ControlFlow
pub enum ControlFlow<B, C = ()> {
Continue(C),
Break(B),
}
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));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, 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(())
}
}Variants
Continue(C)
Move on to the next phase of the operation as normal.
Tuple Fields of Continue
0: CBreak(B)
Exit the operation without running subsequent phases.
Tuple Fields of Break
0: BImplementations
impl<B, C> ControlFlow<B, C>
pub fn is_break(&self) -> bool
control_flow_enum #75744)new API
Returns true if this is a Break variant.
Examples
#![feature(control_flow_enum)] use std::ops::ControlFlow; assert!(ControlFlow::<i32, String>::Break(3).is_break()); assert!(!ControlFlow::<String, i32>::Continue(3).is_break());
pub fn is_continue(&self) -> bool
control_flow_enum #75744)new API
Returns true if this is a Continue variant.
Examples
#![feature(control_flow_enum)] use std::ops::ControlFlow; assert!(!ControlFlow::<i32, String>::Break(3).is_continue()); assert!(ControlFlow::<String, i32>::Continue(3).is_continue());
pub fn break_value(self) -> Option<B>
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);
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.
impl<B> ControlFlow<B, ()>
pub const CONTINUE: ControlFlow<B, ()>
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));impl<C> ControlFlow<(), C>
pub const BREAK: ControlFlow<(), C>
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);Trait Implementations
pub fn clone(&self) -> ControlFlow<B, C>
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source. Read more
pub fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>
Formats the value using the given formatter. Read more
impl<B, C> FromResidual<<ControlFlow<B, C> as Try>::Residual> for ControlFlow<B, C>
pub fn from_residual(residual: ControlFlow<B, Infallible>) -> ControlFlow<B, C>
Constructs the type from a compatible Residual type. Read more
pub fn eq(&self, other: &ControlFlow<B, C>) -> bool
This method tests for self and other values to be equal, and is used by ==. Read more
pub fn ne(&self, other: &ControlFlow<B, C>) -> bool
This method tests for !=.
impl<B, C> Try for ControlFlow<B, C>
type Output = C
The type of the value produced by ? when not short-circuiting.
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 from_output(
output: <ControlFlow<B, C> as Try>::Output
) -> ControlFlow<B, C>
Constructs the type from its Output type. Read more
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
impl<B, C> StructuralPartialEq for ControlFlow<B, C>
Auto Trait Implementations
impl<B, C> RefUnwindSafe for ControlFlow<B, C> where
B: RefUnwindSafe,
C: RefUnwindSafe,
impl<B, C> UnwindSafe for ControlFlow<B, C> where
B: UnwindSafe,
C: UnwindSafe,
Blanket Implementations
impl<T> From<T> for T
pub fn from(t: T) -> T
Performs the conversion.
pub fn into(self) -> U
Performs the conversion.
type Owned = T
The resulting type after obtaining ownership.
pub fn to_owned(&self) -> T
Creates owned data from borrowed data, usually by cloning. Read more
pub fn clone_into(&self, target: &mut T)
toowned_clone_into #41263)recently added
Uses borrowed data to replace owned data, usually by cloning. Read more
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
Performs the conversion.
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
Performs the conversion.
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/ops/enum.ControlFlow.html