问题描述
我想分析传入项目的价值并相应地调整/分组传出项目。为此,我需要确保我的扩展只能在迭代器包装特定类型的项目上调用。
我天真的方法是将项目类型固定在我的扩展特征中:
trait Tags: Sized + Iterator<Item = i32> {
fn tags(self) -> TagsIterator<Self> {
TagsIterator(self)
}
}
impl<I: Sized + Iterator<Item = i32>> Tags for I {}
struct TagGroup;
struct TagsIterator<I: Sized + Iterator<Item = i32>>(I);
impl<I: Sized + Iterator<Item = i32>> Iterator for TagsIterator<I> {
type Item = TagGroup;
fn next(&mut self) -> Option<Self::Item> {
unimplemented!()
}
}
不幸的是它不起作用:
let test = vec![0_i32,1_i32,2_i32];
test.iter().tags();
error[E0599]: the method `tags` exists for struct `std::slice::Iter<'_,i32>`,but its trait bounds were not satisfied
--> src/main.rs:20:17
|
20 | test.iter().tags();
| ^^^^ method cannot be called on `std::slice::Iter<'_,i32>` due to unsatisfied trait bounds
|
= note: the following trait bounds were not satisfied:
`<std::slice::Iter<'_,i32> as Iterator>::Item = i32`
which is required by `std::slice::Iter<'_,i32>: Tags`
`<&std::slice::Iter<'_,i32> as Iterator>::Item = i32`
which is required by `&std::slice::Iter<'_,i32>: Tags`
`&std::slice::Iter<'_,i32>: Iterator`
which is required by `&std::slice::Iter<'_,i32>: Tags`
`<&mut std::slice::Iter<'_,i32> as Iterator>::Item = i32`
which is required by `&mut std::slice::Iter<'_,i32>: Tags`
我做错了什么?限制扩展特征的传入项目类型的正确方法是什么?
解决方法
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