Public deleted or private default ctor/assignment/copy ctor?

Question

If I want to forbid copy construction/assignment then is:

class foo
{
public:
   foo(const foo&) = delete;
   foo& operator = (const foo&) = delete;
};

The same as:

class foo
{
private:
   foo(const foo&) = default;
   foo& operator = (const foo&) = default;
};

Which is the right way and why?

Answer 1

The right way is the first solution : the copy constructor and assignment operators are not defined, so any attempt to use them will not compile.

class foo
{
public:
   foo(const foo&) = delete;
   foo& operator = (const foo&) = delete;
};

---

The second is declaring and defining the implicitly generated forms as private :

• An object of type foo is allowed to copy itself.
• Any friend class or method is also allowed to copy a foo

So copy construction/assignment is still possible.

You could also use boost::noncopyable as a base class, it does exactly that with c++11 (see the source code here)