src/test/ui/rfc1598-generic-associated-types/collections.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#![feature(generic_associated_types)]
//~^ WARNING the feature `generic_associated_types` is incomplete
#![feature(associated_type_defaults)]

// FIXME(#44265): "lifetime parameters are not allowed on this type" errors will be addressed in a
// follow-up PR.

// A Collection trait and collection families. Based on
// http://smallcultfollowing.com/babysteps/blog/2016/11/03/
// associated-type-constructors-part-2-family-traits/

trait Collection<T> {
    type Iter<'iter>: Iterator<Item=&'iter T>;
    type Family: CollectionFamily;
    // Test associated type defaults with parameters
    type Sibling<U>: Collection<U> =
        <<Self as Collection<T>>::Family as CollectionFamily>::Member<U>;
    //~^ ERROR type parameters are not allowed on this type [E0109]

    fn empty() -> Self;

    fn add(&mut self, value: T);

    fn iterate<'iter>(&'iter self) -> Self::Iter<'iter>;
    //~^ ERROR lifetime parameters are not allowed on this type [E0110]
}

trait CollectionFamily {
    type Member<T>: Collection<T, Family = Self>;
}

struct VecFamily;

impl CollectionFamily for VecFamily {
    type Member<T> = Vec<T>;
}

impl<T> Collection<T> for Vec<T> {
    type Iter<'iter> = std::slice::Iter<'iter, T>;
    type Family = VecFamily;

    fn empty() -> Self {
        Vec::new()
    }

    fn add(&mut self, value: T) {
        self.push(value)
    }

    fn iterate<'iter>(&'iter self) -> Self::Iter<'iter> {
    //~^ ERROR lifetime parameters are not allowed on this type [E0110]
        self.iter()
    }
}

fn floatify<C>(ints: &C) -> <<C as Collection<i32>>::Family as CollectionFamily>::Member<f32>
//~^ ERROR type parameters are not allowed on this type [E0109]
where
    C: Collection<i32>,
{
    let mut res = C::Family::Member::<f32>::empty();
    for &v in ints.iterate() {
        res.add(v as f32);
    }
    res
}

fn floatify_sibling<C>(ints: &C) -> <C as Collection<i32>>::Sibling<f32>
//~^ ERROR type parameters are not allowed on this type [E0109]
where
    C: Collection<i32>,
{
    let mut res = C::Family::Member::<f32>::empty();
    for &v in ints.iterate() {
        res.add(v as f32);
    }
    res
}

fn use_floatify() {
    let a = vec![1i32, 2, 3];
    let b = floatify(a);
    println!("{}", b.iterate().next());
    let c = floatify_sibling(a);
    println!("{}", c.iterate().next());
}

fn main() {}