Enum tracing_core::stdlib::ops::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 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§

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Continue(C)

Move on to the next phase of the operation as normal.

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Break(B)

Exit the operation without running subsequent phases.

Implementations§

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impl<B, C> ControlFlow<B, C>

1.59.0 · source

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 · source

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());
source

pub fn break_value(self) -> Option<B>

🔬This is a nightly-only experimental API. (control_flow_enum #75744)

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);
source

pub fn map_break<T, F>(self, f: F) -> ControlFlow<T, C>where F: FnOnce(B) -> T,

🔬This is a nightly-only experimental API. (control_flow_enum #75744)

Maps ControlFlow<B, C> to ControlFlow<T, C> by applying a function to the break value in case it exists.

source

pub fn continue_value(self) -> Option<C>

🔬This is a nightly-only experimental API. (control_flow_enum #75744)

Converts the ControlFlow into an Option which is Some if the ControlFlow was Continue and None otherwise.

Examples
#![feature(control_flow_enum)]
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));
source

pub fn map_continue<T, F>(self, f: F) -> ControlFlow<B, T>where F: FnOnce(C) -> T,

🔬This is a nightly-only experimental API. (control_flow_enum #75744)

Maps ControlFlow<B, C> to ControlFlow<B, T> by applying a function to the continue value in case it exists.

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impl<R> ControlFlow<R, <R as Try>::Output>where R: Try,

This impl block contains no items.

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§

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impl<B, C> Clone for ControlFlow<B, C>where B: Clone, C: Clone,

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fn clone(&self) -> ControlFlow<B, C>

Returns a copy of the value. Read more
1.0.0 · source§

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<B, C> Debug for ControlFlow<B, C>where B: Debug, C: Debug,

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fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
const: unstable · source§

impl<B, C> FromResidual<<ControlFlow<B, C> as Try>::Residual> for ControlFlow<B, C>

const: unstable · source§

fn from_residual(residual: ControlFlow<B, Infallible>) -> ControlFlow<B, C>

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
Constructs the type from a compatible Residual type. Read more
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impl<B, C> Hash for ControlFlow<B, C>where B: Hash, C: Hash,

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fn hash<__H>(&self, state: &mut __H)where __H: Hasher,

Feeds this value into the given Hasher. Read more
1.3.0 · source§

fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl<B, C> PartialEq<ControlFlow<B, C>> for ControlFlow<B, C>where B: PartialEq<B>, C: PartialEq<C>,

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fn eq(&self, other: &ControlFlow<B, C>) -> bool

This method tests for self and other values to be equal, and is used by ==.
1.0.0 · source§

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
const: unstable · source§

impl<B, C> Residual<C> for ControlFlow<B, Infallible>

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type TryType = ControlFlow<B, C>

🔬This is a nightly-only experimental API. (try_trait_v2_residual #91285)
The “return” type of this meta-function.
const: unstable · source§

impl<B, C> Try for ControlFlow<B, C>

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type Output = C

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
The type of the value produced by ? when not short-circuiting.
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type Residual = ControlFlow<B, Infallible>

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
The type of the value passed to FromResidual::from_residual as part of ? when short-circuiting. Read more
const: unstable · source§

fn from_output(output: <ControlFlow<B, C> as Try>::Output) -> ControlFlow<B, C>

🔬This is a nightly-only experimental API. (try_trait_v2 #84277)
Constructs the type from its Output type. Read more
const: unstable · source§

fn branch( self ) -> ControlFlow<<ControlFlow<B, C> as Try>::Residual, <ControlFlow<B, C> as Try>::Output>

🔬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
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impl<B, C> Copy for ControlFlow<B, C>where B: Copy, C: Copy,

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impl<B, C> Eq for ControlFlow<B, C>where B: Eq, C: Eq,

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impl<B, C> StructuralEq for ControlFlow<B, C>

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impl<B, C> StructuralPartialEq for ControlFlow<B, C>

Auto Trait Implementations§

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impl<B, C> RefUnwindSafe for ControlFlow<B, C>where B: RefUnwindSafe, C: RefUnwindSafe,

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impl<B, C> Send for ControlFlow<B, C>where B: Send, C: Send,

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impl<B, C> Sync for ControlFlow<B, C>where B: Sync, C: Sync,

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impl<B, C> Unpin for ControlFlow<B, C>where B: Unpin, C: Unpin,

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impl<B, C> UnwindSafe for ControlFlow<B, C>where B: UnwindSafe, C: UnwindSafe,

Blanket Implementations§

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impl<T> Any for Twhere T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for Twhere T: ?Sized,

const: unstable · source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere T: ?Sized,

const: unstable · source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

const: unstable · source§

fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for Twhere U: From<T>,

const: unstable · source§

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToOwned for Twhere T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
const: unstable · source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
const: unstable · source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.