Generics 类型不匹配：找到了预期的关联类型结构

我有以下示例代码：

trait Manager: Sized {
    type Item: Item<Manager=Self>;
}

trait Item: Sized {
    type Manager: Manager<Item=Self> = DefaultManager<Self>;
}

struct DefaultManager<T: Item<Manager=DefaultManager<T>>>(::std::marker::PhantomData<T>);

impl<T: Item<Manager=DefaultManager<T>>> Manager for DefaultManager<T> {
    type Item = T;
}

到

在这种情况下，

DefaultManager

不应是有效的类型，因为

：：Manager

是

FooManager

，而不是

DefaultManager

导致类型不匹配的原因是什么？我如何向编译器澄清是否满足类型约束

---

编辑：为了澄清，我使用了不稳定的

关联的\u type_defaults

功能，这样我就可以为

Item:：Manager

提供默认值，所以这个示例目前只建立在夜间的基础上。

@Shepmaster很好，我添加了一个澄清。

<anon>:9:5: 9:61 warning: type mismatch resolving `<Self as Item>::Manager == DefaultManager<Self>`: expected associated type, found struct `DefaultManager` [E0271]
<anon>:9     type Manager: Manager<Item=Self> = DefaultManager<Self>;
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<anon>:9:5: 9:61 help: see the detailed explanation for E0271
<anon>:9:5: 9:61 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details.
<anon>:9     type Manager: Manager<Item=Self> = DefaultManager<Self>;
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<anon>:9:5: 9:61 note: required by `DefaultManager`

struct DefaultManager<T: Item<Manager=DefaultManager<T>>>(...)

struct DefaultMananger<T: Item>

struct Foo;
impl Item for Foo { type Manager = FooManager; }

struct FooManager;
impl Manager for FooManager { type Item = Foo; }

type DefaultFooManager = DefaultManager<Foo>;