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#![deny(unused_must_use)]
#![feature(arbitrary_self_types)]
use std::iter::Iterator;
use std::future::Future;
use std::task::{Context, Poll};
use std::pin::Pin;
use std::unimplemented;
struct MyFuture;
impl Future for MyFuture {
type Output = u32;
fn poll(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<u32> {
Poll::Pending
}
}
fn iterator() -> impl Iterator {
std::iter::empty::<u32>()
}
fn future() -> impl Future {
MyFuture
}
fn square_fn_once() -> impl FnOnce(u32) -> u32 {
|x| x * x
}
fn square_fn_mut() -> impl FnMut(u32) -> u32 {
|x| x * x
}
fn square_fn() -> impl Fn(u32) -> u32 {
|x| x * x
}
fn main() {
iterator(); //~ ERROR unused implementer of `Iterator` that must be used
future(); //~ ERROR unused implementer of `Future` that must be used
square_fn_once(); //~ ERROR unused implementer of `FnOnce` that must be used
square_fn_mut(); //~ ERROR unused implementer of `FnMut` that must be used
square_fn(); //~ ERROR unused implementer of `Fn` that must be used
}
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