有没有一种方法可以为容器类型创建操作符/函数重载

Question

I have some class like:

class A {
A& operator=(const A& a);
A& operator=(const int a);
A& operator=(const std::string& a);
};

I made type trait for iterable is_iterable ; How to implement overload for operator= for iterable types?

My approach:

template<typename TContainer, std::enable_if_t<is_iterable<TContainer>::value>>
A& operator=(const TContainer& val) {
// do stuff
}

but it doesn't work causing no viable overload error when i try to feed std::list or std::vector .

So, how to fix it and is it possible to use that kind of overload?

Answer 1

When is_iterable<TContainer>::value is true, std::enable_if_t<is_iterable<TContainer>::value> is void , which is not a valid non-type template parameter. Define your container overload as

template<typename TContainer,
         std::enable_if_t<is_iterable<TContainer>{}, int*> = nullptr>
A& operator=(const TContainer&)

Live demo

Answer 2

Not sure if it is what you are looking for but I believe:

template<typename TContainer>
A& operator=(const TContainer& container) {
    for (auto it = container.begin(); it != container.end(); it++) {
        // do stuff
    }
    return *this;
}

The template will be called only if other overloads does not match to type fed. If the type is not iterable, and error will occur on call to begin() and end() .