mirror of https://github.com/rust-lang/rust
70 lines
1.5 KiB
Rust
70 lines
1.5 KiB
Rust
#![feature(associated_type_defaults)]
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// A Collection trait and collection families. Based on
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// https://smallcultfollowing.com/babysteps/blog/2016/11/03/
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// associated-type-constructors-part-2-family-traits/
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//@ run-pass
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trait Collection<T> {
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type Iter<'iter>: Iterator<Item=&'iter T> where T: 'iter, Self: 'iter;
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type Family: CollectionFamily;
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// Test associated type defaults with parameters
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type Sibling<U>: Collection<U> =
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<<Self as Collection<T>>::Family as CollectionFamily>::Member<U>;
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fn empty() -> Self;
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fn add(&mut self, value: T);
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fn iterate<'iter>(&'iter self) -> Self::Iter<'iter>;
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}
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trait CollectionFamily {
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type Member<T>: Collection<T, Family = Self>;
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}
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struct VecFamily;
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impl CollectionFamily for VecFamily {
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type Member<T> = Vec<T>;
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}
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impl<T> Collection<T> for Vec<T> {
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type Iter<'iter> = std::slice::Iter<'iter, T> where T: 'iter;
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type Family = VecFamily;
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fn empty() -> Self {
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Vec::new()
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}
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fn add(&mut self, value: T) {
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self.push(value)
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}
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fn iterate<'iter>(&'iter self) -> Self::Iter<'iter> {
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self.iter()
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}
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}
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fn floatify<C>(ints: &C) -> <<C as Collection<i32>>::Family as CollectionFamily>::Member<f32>
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where
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C: Collection<i32>,
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{
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let mut res = <C::Family as CollectionFamily>::Member::<f32>::empty();
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for &v in ints.iterate() {
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res.add(v as f32);
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}
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res
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}
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fn use_floatify() {
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let a = vec![1, 2, 3];
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let b = floatify(&a);
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assert_eq!(Some(&1.0), b.iterate().next());
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}
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fn main() {
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use_floatify();
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}
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