我可以将具有非常量值类型的映射转换为具有常量值类型的映射吗？

Question

I have something like the following:

map<int, StructType> map;
const map<int, StructType>& GetMap() { return map; }

I'd like to do something along these lines:

const map<int, const StructType>& GetConstMap() { return map; }

Is there any way I can add this const -ness to the value type of the map?

Answer 1

The interface of std::map is designed so that const map<K,T> effectively has a const value type, by never exposing non-const access to its elements.

So you cannot add, remove or modify elements through a const map reference.

So:

struct X
{
    map<int, StructType> m;

    const map<int, StructType>& GetConstMap() const { return m; }
}

Is what you want.