Overloading assignment operator in a class template [closed]

Answer 1

I think this is what you're looking for. You're assigning a T2 to a T. That means we need to take a Number<T2>, cast the value to T, then assign to this and return *this.

template <class T2 >
Number<T>& operator=( const Number<T2>& number )
{
  m_value = T( number.value() );

  return *this;
}

Answer 2

Maybe you just want to overload your operator='s:

template <class T2>
Number<T>& operator=( const Number<T2*>& number )
{
    // Deep Copy
}

template <class T2>
Number<T>& operator=( const Number<T2>& number )
{
    // Shallow Copy
}

In probably all other cases you want std::enable_if to statically decide which copy stategy shall be used depending on the type (most likely whether it is a pointer type, therefore e.g. std::is_pointer<T2>::value). This can then very easily simplified by if constexpr (C++17):

#include <type_traits>

template <class T2>
Number<T>& operator=( const Number<T2>& number )
{
    if constexpr( std::is_pointer_v<T2> ){
        // Deep Copy
    }
    else{
        // Shallow Copy
    }
    return *this;
}

Hope this helps!