How to declare a lifetime for a closure argument?

Question

I would like to declare a lifetime for a closure in Rust, but I can\'t find a way to add a lifetime declaration.

use std::str::SplitWhitespace;

pub struct P         


        

Answer 1

The &mut SplitWhitespace is actually a &'b mut SplitWhitespace<'a>. The relevant lifetime here is the 'a, as it specifies how long the string slices that next returns live. Since you applied the split_whitespace function on your line argument, you need to set 'a to the same lifetime that the line argument has.

So as a first step you add a lifetime to line:

fn process_string<'a>(line: &'a str, line_number: usize) -> Result<(), ParserError> {

and then you add the lifetime to the type in your closure:

let nt = |t: &mut SplitWhitespace<'a>| t.next().ok_or(missing_token(line_number));

Note that while this answers your question, the correct solution to your Problem is @A.B.'s solution.