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ControlFlow in std::ops - Rust

 2 years ago
source link: https://doc.rust-lang.org/stable/std/ops/enum.ControlFlow.html
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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));
Run

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(())
    }
}
Run

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