我正在尝试用特征和相关类型在 Rust 上实现一些东西。我不知道如何用文字来表达我的问题,所以我将添加一个代码片段,希望能说明我正在尝试做的事情。
pub trait Person {}
pub trait Directory<P: Person> {
type Per = P;
fn get_person(&self) -> Self::Per;
}
pub trait Catalog {
type Per : Person;
type Dir : Directory<Self::Per>;
fn get_directory(&self) -> Self::Dir;
}
fn do_something<C>(catalog: C) where C: Catalog {
let directory : C::Dir = catalog.get_directory();
// let person : C::Per = directory.get_person();
// The code above fails with:
// error: mismatched types:
// expected `<C as Catalog>::Per`,
// found `<<C as Catalog>::Dir as Directory<<C as Catalog>::Per>>::Per`
// (expected trait `Catalog`,
// found trait `Directory`) [E0308]
let person = directory.get_person();
do_something_with_person(person);
}
fn do_something_with_person<P: Person>(p: P) {}
我希望上面的代码可以编译,但事实并非如此。
相反,我得到:
error: the trait `Person` is not implemented for the type `<<C as Catalog>::Dir as Directory<<C as Catalog>::Per>>::Per` [E0277]
其中,AFAICT 意味着编译器无法确定 person 变量具有 Person 特征。
我正在使用以下 rustc 版本:
rustc 1.2.0-dev (a19ed8ad1 2015-06-18)
我错过了什么吗?