如何用签名`object()模拟函数`

A::B X(void) . 定义如下。

class A {
    class B;
    virtual B X() = 0;
};

class A::B {
  public:
    auto_ptr<int> something;
};

class mA : public A
{
  public:
    MOCK_METHOD0(X, A::B());
};

然而,这给了我一个奇怪的错误,我还没能找到它。这有什么问题?

In member function ‘virtual A::B mA::X()’:
...: error: no matching function for call to ‘A::B::B(A::B)’
...: note: candidates are: A::B::B()
...:                       A::B::B(A::B&)

我找到了一个失败的代码示例来演示这一点。

#include <gmock/gmock.h>
#include <memory>
using std::auto_ptr;

class thing {
  public:
    class result;
    virtual result accessor () = 0;
};

class thing::result {
    auto_ptr<int> x;   // If this just "int", error goes away.
};

namespace mock {
    class thing : ::thing {
      public:
        MOCK_METHOD0 ( accessor, result() );
    };
}