rust/src/test/ui/variance-iterators-in-libcore.rs

// run-pass

#![allow(warnings)]

use std::iter::Zip;

fn zip_covariant<'a, A, B>(iter: Zip<&'static A, &'static B>) -> Zip<&'a A, &'a B> { iter }

fn main() { }
tests: Add missing run-pass annotations 2019-07-26 16:54:25 -05:00			`// run-pass`

Remove data structure specialization for .zip() iterator Go back on half the specialization, the part that changed the Zip struct's fields themselves depending on the types of the iterators. This means that the Zip iterator will always carry two usize fields, which are unused. If a whole for loop using a .zip() iterator is inlined, these are simply removed and have no effect. The same improvement for Zip of for example slice iterators remain, and they still optimize well. However, like when the specialization of zip was merged, the compiler is still very sensistive to the exact context. For example this code only autovectorizes if the function is used, not if the code in zip_sum_i32 is inserted inline it was called: ``` fn zip_sum_i32(xs: &[i32], ys: &[i32]) -> i32 { let mut s = 0; for (&x, &y) in xs.iter().zip(ys) { s += x * y; } s } fn zipdot_i32_default_zip(b: &mut test::Bencher) { let xs = vec![1; 1024]; let ys = vec![1; 1024]; b.iter(\|\| { zip_sum_i32(&xs, &ys) }) } ``` Include a test that checks that Zip<T, U> is covariant w.r.t. T and U. 2016-09-15 02:59:55 -05:00			`#![allow(warnings)]`

			`use std::iter::Zip;`

			`fn zip_covariant<'a, A, B>(iter: Zip<&'static A, &'static B>) -> Zip<&'a A, &'a B> { iter }`

			`fn main() { }`