Borrow checker doesn't realize that `clear` drops reference to local variable

Question

The following code reads space-delimited records from stdin, and writes comma-delimited records to stdout. Even with optimized builds it\'s rather slow (about twice as slow

Answer 1

Itertools has .format() for the purpose of lazy formatting, which skips allocating a string too.

use std::io::BufRead;
use itertools::Itertools;

fn main() {
    let stdin = std::io::stdin();
    for line in stdin.lock().lines().map(|x| x.unwrap()) {
        println!("{}", line.split(' ').format(","));
    }
}

---

A digression, something like this is a “safe abstraction” in the littlest sense of the solution in another answer here:

fn repurpose<'a, T: ?Sized>(mut v: Vec<&T>) -> Vec<&'a T> {
    v.clear();
    unsafe {
        transmute(v)
    }
}