src/test/ui/lint/unused/must_use-in-stdlib-traits.rs

   1 #![deny(unused_must_use)]
   2 #![feature(arbitrary_self_types)]
   3
   4 use std::iter::Iterator;
   5 use std::future::Future;
   6
   7 use std::task::{Context, Poll};
   8 use std::pin::Pin;
   9 use std::unimplemented;
  10
  11 struct MyFuture;
  12
  13 impl Future for MyFuture {
  14    type Output = u32;
  15
  16    fn poll(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<u32> {
  17       Poll::Pending
  18    }
  19 }
  20
  21 fn iterator() -> impl Iterator {
  22    std::iter::empty::<u32>()
  23 }
  24
  25 fn future() -> impl Future {
  26    MyFuture
  27 }
  28
  29 fn square_fn_once() -> impl FnOnce(u32) -> u32 {
  30    |x| x * x
  31 }
  32
  33 fn square_fn_mut() -> impl FnMut(u32) -> u32 {
  34    |x| x * x
  35 }
  36
  37 fn square_fn() -> impl Fn(u32) -> u32 {
  38    |x| x * x
  39 }
  40
  41 fn main() {
  42    iterator(); //~ ERROR unused implementer of `Iterator` that must be used
  43    future(); //~ ERROR unused implementer of `Future` that must be used
  44    square_fn_once(); //~ ERROR unused implementer of `FnOnce` that must be used
  45    square_fn_mut(); //~ ERROR unused implementer of `FnMut` that must be used
  46    square_fn(); //~ ERROR unused implementer of `Fn` that must be used
  47 }