ABC虚拟OStream插入操作符

Question

请考虑以下代码段:

struct ObjectInterface
{
    virtual ~ObjectInterface() {}
    virtual void Print(std::ostream& target) const = 0;
};

struct Foo : ObjectInterface
{
    virtual void Print(std::ostream& target) const
    {
        target << "Foo";
    }
};

struct Bar : ObjectInterface
{
    virtual void Print(std::ostream& target) const
    {
        target << "Bar";
    }
};

有没有办法改变Print的ObjectInterface,以标准的" std::ostream& operator<<"输出型？我不能让它发挥作用.

编辑:我基本上想弄清楚我是否可以friend合作virtual.

Answer 1

你需要一个免费的功能:

ostream & operator << ( ostream & os, const ObjectInterface & oi ) {
    oi.Print( os );
    return os;
}