Can I prevent a copy constructor with some exception?

Question

I will use std::map<int, A>

A is a class and I have to prevent shallow copy, but there are many classes like A, so making a deep copy construct and operator is tiresome. Since it seems that I don't have to use copy constructor and copy assignment operator, I decide not to use them.

To prevent some mistakes, I made UnCopyable class, which has private copy constuctor and copy assignment operator, and A inherited it.

However, there is one problem. std::map use a copy constructor.

I don't want to save A's pointer in the map.

What's the better solution?

Answer 1

You could use a smart pointer like std::shared_ptr or write a proxy class.

E.g.:

class Foo {
public:
    std::string name() const;
};

typedef std::shared_ptr<Foo> SharedFoo;

or

class SharedFoo {
public:
    std::string name() const { return instance->name(); }
private:
    std::shared_ptr<Foo> instance;
};

Answer 2

You might think about trying C++11, which has a couple solutions to this kind of problem: std::map::emplace which eliminates the Copyable requirement for A, and std::move which allows you to transfer one object into another without copying.

Also, there is a new, more explicit way to define a class as non-copyable:

A( A const & ) = delete;

It's a good time to upgrade your C++ compiler.