编译器何时可以将调用静态绑定到虚函数?

Should I expect the compiler to statically bind the calls to f() in Case 2) below? Is the "reference"ness of cr somehow propagating to cr.a even though a is an A and not an A&?

struct A
{
    virtual void f() ;
    virtual ~A() ;
};

struct B : A
{
    virtual void f() ;
    virtual ~B() ;
};

struct C {
    A a ;
    B b ;
};

C & GetACRef() ;

void test()
{
    // Case 1) The following calls to f() are statically bound i.e.
    // f() is called without looking up the virtual function ptr.
    C c ;  
    c.a.f() ;
    c.b.f() ;
    A a ;
    a.f() ;

    // Case 2) The following calls to f() go through the dynamic dispatching
    // virtual function lookup code. You can check if you generate the .asm
    // for this file.
    C & cr = GetACRef() ; // Note that C is not polymorphic
    cr.a.f() ; // visual C++ 2010 generates call to f using virtual dispatching
    cr.b.f() ; // visual C++ 2010 generates call to f using virtual dispatching  
}

推荐答案

我不知道为什么 MSVC 不将您的案例 2"场景编译为直接调用 - 这当然是可能的.我认为只有微软才能回答.

A a;
A& ar(a);
ar.f();