default_0_delete_meaning.cpp

// Default constructors

class foo {
public:
  /*
  =0
  C++ uses the special syntax = 0; to indicate pure virtual functions instead of
  adding a new keyword to the language
  */
  void virtual pureVirtualFunction() = 0;
  /*
  =default
  It means that you want to use the compiler-generated version of that function,
  so you don't need to specify a body.
  */
  ~foo() = default;
  /*
  = delete
      It means that the compiler will not generate those constructors for you.
  This is only allowed on copy constructor and assignment operator
  */
  foo(const foo &t) = delete;
  foo &operator=(const foo &t) = delete;
};

int main() {
  // foo
}