Can changing from private constructor/assignment operator to deleted break binary compatibility?

Question

Using C++11.

I have a class I want to clean-up a bit by making the following changes:

From

class MyClass {
public:
  // code
private:
  MyClass(const MyClass&);
  MyClass& operator=(const MyClass&);
  // members
};

To

class MyClass {
public:
  // code
  MyClass(const MyClass&) = delete;
  MyClass& operator=(const MyClass&) = delete;
private:
  // members
};

Knowing that both are declared but not defined, will this change break binary compatibility? Does it improves anything?

Answer 1

If you switch from your first version to the second, where you have accessible, user-declared, deleted constructors, code like this will compile in C++11:

MyClass b{};

But if you upgrade to C++20, it won't. That might not be something you want. If you stick with your first version, where the constructors are inaccessible, the declaration of b won't compile in any language version, so you won't have this problem at least.

Here's a demo.