Why does the lifetime name appear as part of the function type?

Question

I believe that this function declaration tells Rust that the lifetime of the function\'s output is the same as the lifetime of it\'s s parameter:

fn         


        

Answer 1

The <'a> annotation just declares the lifetimes used in the function, exactly like generic parameters .

fn subslice<'a, T>(s: &'a [T], until: u32) -> &'a [T] { \\'
    &s[..until as usize]
}

Note that in your example, all lifetimes can be inferred.

fn subslice(s: &[T], until: u32) -> &[T] {
    &s[..until as usize]
}

fn substr(s: &str, until: u32) -> &str {
    &s[..until as usize]
}

playpen example