Access the methods of primitive Rust types

Question

How can I access the methods of primitive types in Rust?

Concretely, I want to pass either one of the two slice methods split_first_mut and split_last_mut to a function operating on slices. I know you can wrap them in closures as a workaround, but I'd like to know if direct access is possible.

Answer 1

You can access the methods on primitives just like regular types:

u8::to_le();
str::from_utf8();
<[_]>::split_first_mut();

You can create a function that accepts a slice ops function:

fn do_thing<T>(f: impl Fn(&mut [u8])) -> Option<(&mut T, &mut [T])>) {
    // ...
}

And pass in both split_first_mut and split_last_mut :

fn main() {
    do_thing(<[_]>::split_first_mut);
    do_thing(<[_]>::split_last_mut);
}

Answer 2

You have to refer to the method using fully-qualified syntax. In a nutshell: <T>::{method_name} where T is the type and {method_name} is the name of the method. For example, if you're modifying a [i32] then you'd to prefix the method name with <[i32]>:: like this:

fn apply_fn<T, U>(t: T, t_fn: fn(T) -> U) -> U {
    t_fn(t)
}

fn main() {
    let mut items: Vec<i32> = vec![1, 2, 3];

    let slice: &mut [i32] = items.as_mut_slice();
    let first_split = apply_fn(slice, <[i32]>::split_first_mut);

    let slice: &mut [i32] = items.as_mut_slice();
    let last_split = apply_fn(slice, <[i32]>::split_last_mut);
}

playground