src/test/ui/generic-associated-types/collections-project-default.rs

   1 #![allow(incomplete_features)]
   2 #![feature(generic_associated_types)]
   3 #![feature(associated_type_defaults)]
   4
   5 // A Collection trait and collection families. Based on
   6 // http://smallcultfollowing.com/babysteps/blog/2016/11/03/
   7 // associated-type-constructors-part-2-family-traits/
   8
   9 // check that we don't normalize with trait defaults.
  10
  11 trait Collection<T> {
  12     type Iter<'iter>: Iterator<Item=&'iter T> where T: 'iter;
  13     type Family: CollectionFamily;
  14     // Test associated type defaults with parameters
  15     type Sibling<U>: Collection<U> =
  16         <<Self as Collection<T>>::Family as CollectionFamily>::Member<U>;
  17
  18     fn empty() -> Self;
  19
  20     fn add(&mut self, value: T);
  21
  22     fn iterate<'iter>(&'iter self) -> Self::Iter<'iter>;
  23 }
  24
  25 trait CollectionFamily {
  26     type Member<T>: Collection<T, Family = Self>;
  27 }
  28
  29 struct VecFamily;
  30
  31 impl CollectionFamily for VecFamily {
  32     type Member<T> = Vec<T>;
  33 }
  34
  35 impl<T> Collection<T> for Vec<T> {
  36     type Iter<'iter> where T: 'iter = std::slice::Iter<'iter, T>;
  37     type Family = VecFamily;
  38
  39     fn empty() -> Self {
  40         Vec::new()
  41     }
  42
  43     fn add(&mut self, value: T) {
  44         self.push(value)
  45     }
  46
  47     fn iterate<'iter>(&'iter self) -> Self::Iter<'iter> {
  48         self.iter()
  49     }
  50 }
  51
  52 fn floatify_sibling<C>(ints: &C) -> <C as Collection<i32>>::Sibling<f32>
  53 where
  54     C: Collection<i32>,
  55 {
  56     let mut res = <C::Family as CollectionFamily>::Member::<f32>::empty();
  57     for &v in ints.iterate() {
  58         res.add(v as f32);
  59     }
  60     res
  61     //~^ ERROR mismatched types
  62 }
  63
  64 fn use_floatify() {
  65     let a = vec![1i32, 2, 3];
  66     let c = floatify_sibling(&a);
  67     assert_eq!(Some(&1.0), c.iterate().next());
  68 }
  69
  70 fn main() {
  71     use_floatify();
  72 }