Inheriting classes from std::

Question

There are many similar questions and I found both pro and against reasons to use this pattern so I am asking this here:

I need to make a JSON implementation in C++ (

Answer 1

is there any specific reason why not to do this?

Yes. What you obtain with this, is UB. The problem arises from the std:: containers not supporting polymorphism. They were not designed to be inherited from (no virtual destructor) and this means you cannot write a correct/safe destructor sequence.

Instead, your solution probably should look like this:

namespace XYZ { // <-- cannot have same name as class here
    class JSON { };
    class object : public JSON {
        std::unordered_map values;
    public:
        JSON& operator[]( const std::string& key );
    };
    class vector : public JSON {
        // same here
    };
  ...
};