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#![feature(generic_associated_types)]
//~^ WARNING the feature `generic_associated_types` is incomplete
// FIXME(#44265): "lifetime argument not allowed on this type" errors will be addressed in a
// follow-up PR
use std::fmt::Display;
trait StreamingIterator {
type Item<'a>;
// Applying the lifetime parameter `'a` to `Self::Item` inside the trait.
fn next<'a>(&'a self) -> Option<Self::Item<'a>>;
//~^ ERROR lifetime arguments are not allowed for this type [E0109]
}
struct Foo<T: StreamingIterator> {
// Applying a concrete lifetime to the constructor outside the trait.
bar: <T as StreamingIterator>::Item<'static>,
//~^ ERROR lifetime arguments are not allowed for this type [E0109]
}
// Users can bound parameters by the type constructed by that trait's associated type constructor
// of a trait using HRTB. Both type equality bounds and trait bounds of this kind are valid:
//FIXME(sunjay): This next line should parse and be valid
//fn foo<T: for<'a> StreamingIterator<Item<'a>=&'a [i32]>>(iter: T) { /* ... */ }
fn foo<T>(iter: T) where T: StreamingIterator, for<'a> T::Item<'a>: Display { /* ... */ }
//~^ ERROR lifetime arguments are not allowed for this type [E0109]
// Full example of enumerate iterator
#[must_use = "iterators are lazy and do nothing unless consumed"]
struct StreamEnumerate<I> {
iter: I,
count: usize,
}
impl<I: StreamingIterator> StreamingIterator for StreamEnumerate<I> {
type Item<'a> = (usize, I::Item<'a>);
//~^ ERROR lifetime arguments are not allowed for this type [E0109]
fn next<'a>(&'a self) -> Option<Self::Item<'a>> {
//~^ ERROR lifetime arguments are not allowed for this type [E0109]
match self.iter.next() {
None => None,
Some(val) => {
let r = Some((self.count, val));
self.count += 1;
r
}
}
}
}
impl<I> StreamEnumerate<I> {
pub fn new(iter: I) -> Self {
StreamEnumerate {
count: 0,
iter: iter,
}
}
}
fn test_stream_enumerate() {
let v = vec!["a", "b", "c"];
let se = StreamEnumerate::new(v.iter());
let a: &str = se.next().unwrap().1;
for (i, s) in se {
println!("{} {}", i, s);
}
println!("{}", a);
}
fn main() {}
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