不明确的类型引用 [英] Ambiguous type reference

问题描述

为什么会这样:

template <typename T> 
struct foo
{
};

struct A
{
    typedef foo<A> type;
};

struct B : public A
{
    typedef foo<B> type;
};

int main()
{
    B::type john;
    return 0;
}

但不是这个:

template <typename T> 
struct foo
{
};

template <typename T>
struct Shared
{
    typedef foo<T> type;
};

struct A : public Shared<A>
{
};

struct B : public A, public Shared<B>
{
};

int main()
{
    // g++ 4.5 says :
    // error: reference to 'type' is ambiguous
    B::type john;
    return 0;
}

在我的代码中，foo 实际上是 boost::shared_ptr 并且，正如你所看到的，我正在尝试考虑一些 typedefs 使用 Shared 类.

In my code, foo is actually boost::shared_ptr and, as you can see, I'm trying so factor some typedefs using a Shared class.

推荐答案

因为 B 继承了 foo 并且间接地继承了 foo，并且都包含一个成员 type.你说的是哪个?

Because B inherits foo<B> and, indirectly, foo<A>, and both contain a member type. Which did you mean?

你简单的第一段代码有 B 的 type 隐藏 A 的 type，但这不会发生在更复杂的第二段代码中，它涉及更深的继承树.

Your simple, first piece of code has B's type hiding A's type, but that doesn't happen in the more complex second piece of code, which involves a deeper inheritance tree.

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