operator= and functions that are not inherited in C++?

Question

Until a test I've just made, I believed that only Constructors were not inherited in C++. But apparently, the assignment operator= is not too...

1. What is the reason of that ?
2. Is there any workaround to inherit the assignment operator ?
3. Is it also the case for operator+=, operator-=, ... ?
4. Are all other functions (apart from constructors/operator=) inherited ?

In fact, I encountered this problem as I was doing some CRTP :

template<class Crtp> class Base {     inline Crtp& operator=(const Base<Crtp>& rhs) {/*SOMETHING*/; return static_cast<Crtp&>(*this);} };  class Derived1 : public Base<Derived1> { };  class Derived2 : public Base<Derived2> { }; 

Is there any solution to get that working ?

EDIT : OK, I have isolated the problem. Why the following isn't working ? How to solve the problem ?

#include <iostream> #include <type_traits>  // Base class template<template<typename, unsigned int> class CRTP, typename T, unsigned int N> class Base {     // Cast to base     public:         inline Base<CRTP, T, N>& operator()()         {             return *this;         }      // Operator =     public:         template<typename T0, class = typename std::enable_if<std::is_convertible<T0, T>::value>::type>         inline CRTP<T, N>& operator=(const T0& rhs)         {             for (unsigned int i = 0; i < N; ++i) {                 _data[i] = rhs;             }             return static_cast<CRTP<T, N>&>(*this);         }      // Data members     protected:         T _data[N]; };  // Derived class template<typename T, unsigned int N> class Derived : public Base<Derived, T, N> { };  // Main int main() {     Derived<double, 3> x;     x() = 3; // <- This is OK     x = 3;   // <- error: no match for 'operator=' in ' x=3 '     return 0; } 

Answer 1

The assignment operator is technically inherited; however, it is always hidden by an explicitly or implicitly defined assignment operator for the derived class (see comments below).

(13.5.3 Assignment) An assignment operator shall be implemented by a non-static member function with exactly one parameter. Because a copy assignment operator operator= is implicitly declared for a a class if not declared by the user, a base class assignment operator is always hidden by the copy assignment operator of the derived class.

You can implement a dummy assignment operator which simply forwards the call to the base class operator=, like this:

// Derived class template<typename T, unsigned int N> class Derived : public Base<Derived, T, N> { public:     template<typename T0, class = typename std::enable_if<std::is_convertible<T0, T>::value>::type>     inline Derived& operator=(const T0& rhs)     {         return Base<Derived, T, N>::operator=(rhs);     } }; 

Answer 2

The assignment operator is inherited, sort of, but... In any given class, if you do not provide a copy assignment operator, the compiler generates one for you. That means that your derived classes effectively have an assignment operator:

Derived& operator=( Derived const& ); 

And the usual hiding rules apply; this hides all of the base class assignment operators. (If the base class had an assignment operator with this signature, the derived class would inherit it normally.)