| #![allow(incomplete_features)] |
| #![feature(generic_associated_types)] |
| #![feature(associated_type_defaults)] |
| |
| // A Collection trait and collection families. Based on |
| // http://smallcultfollowing.com/babysteps/blog/2016/11/03/ |
| // associated-type-constructors-part-2-family-traits/ |
| |
| // check that we don't normalize with trait defaults. |
| |
| trait Collection<T> { |
| type Iter<'iter>: Iterator<Item=&'iter T> where T: 'iter; |
| type Family: CollectionFamily; |
| // Test associated type defaults with parameters |
| type Sibling<U>: Collection<U> = |
| <<Self as Collection<T>>::Family as CollectionFamily>::Member<U>; |
| |
| fn empty() -> Self; |
| |
| fn add(&mut self, value: T); |
| |
| fn iterate<'iter>(&'iter self) -> Self::Iter<'iter>; |
| } |
| |
| 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> where T: '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> { |
| self.iter() |
| } |
| } |
| |
| fn floatify_sibling<C>(ints: &C) -> <C as Collection<i32>>::Sibling<f32> |
| where |
| C: Collection<i32>, |
| { |
| let mut res = <C::Family as CollectionFamily>::Member::<f32>::empty(); |
| for &v in ints.iterate() { |
| res.add(v as f32); |
| } |
| res |
| //~^ ERROR mismatched types |
| } |
| |
| fn use_floatify() { |
| let a = vec![1i32, 2, 3]; |
| let c = floatify_sibling(&a); |
| assert_eq!(Some(&1.0), c.iterate().next()); |
| } |
| |
| fn main() { |
| use_floatify(); |
| } |