c++ - 类主体中定义的内联友元函数

Question

通常当我们直接在类体中定义一个成员函数时，它是隐式的内联。但是这个呢:

class Foo {
public:
    friend void swap(Foo& a, Foo& b) { ... }

    ...
};

swap 是否隐式内联？

Answer 1

是的。请参阅标准中的 [class.friend/6-7]:

A function can be defined in a friend declaration of a class if and only if the class is a non-local class (9.8), the function name is unqualified, and the function has namespace scope.

Such a function is implicitly inline.