重载运算符<<嵌套的私有类可能吗? [英] Overloading operator<< for a nested private class possible?

问题描述

如何使操作员超负荷<<像这样的嵌套私人班级?

How one can overload an operator<< for a nested private class like this one?

class outer {
  private:
    class nested {
       friend ostream& operator<<(ostream& os, const nested& a);
    };
  // ...
};

在外部类之外尝试时，编译器会抱怨隐私:

When trying outside of outer class compiler complains about privacy:

error: ‘class outer::nested’ is private

推荐答案

您也可以将operator<<设为outer的朋友.或者你 可以在nested中完全实现inline，例如:

You could make the operator<< a friend of outer as well. Or you could implement it completely inline in nested, e.g.:

class Outer
{
    class Inner
    {
        friend std::ostream& 
        operator<<( std::ostream& dest, Inner const& obj )
        {
            obj.print( dest );
            return dest;
        }
        //  ...
        //  don't forget to define print (which needn't be inline)
    };
    //  ...
};

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