Calling closures in a Vec

Published: June 21, 2014

Revised: January 21, 2019 in a029167

In rust one might want to have a list of closures, for example as a list of callbacks.

let mut fs: Vec<||> = Vec::new();
fs.push(|| { println!("imma firing my lazer"); });

for f in fs.iter() {
    f(); // error: expected function but found `&||`
};

Maybe if we borrow f?

for &f in fs.iter() { // error: cannot move out of dereference of `&`-pointer```
    f();
};

But then if we dereference f?

for f in fs.iter() {
    (*f)(); // error: closure invocation in a `&` reference
};

That’s not very helpful. Thanks to some friendly guys over at #rust at irc.mozilla.org I found something which works:

for f in fs.mut_iter() {
    (*f)(); // ok!
};

A note is that the closure types must be &mut || and not &||.

In the end I think that the error messages could be more clear. But now we have a running example and all is well in the world!

// Print "imma firing my lazer"
fn main() {
    let mut fs: Vec<||> = Vec::new();
    fs.push(|| { println!("imma firing my lazer"); });

    for f in fs.mut_iter() {
        (*f)(); // ok!
    };
}