Overloading assignment operator in a class template that can cast to another template type

Question

#ifndef NUMBER_HPP
#define NUMBER_HPP

template 
class Number
{
public:
  Number( T value ) : m_value( value )
  {
  }

  T value() const
  {
    retu         


        

Answer 1

You should do this:

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

That is, use T2 in the parameter type, not in the return type!

I would rather use different letter for template parameter:

template <class U>
Number<T>& operator=( const Number<U>& number )
{
    m_value = number.m_value; //I would also directly access the member variable!
    return *this;
}

I think, it is better to use explicit cast, if you want to use class type as template argument and whose constructor has been declared explicit:

 m_value = static_cast<T>(number.m_value); 

---

By the way, the other operator= should be implemented as:

Number<T>& operator=(T const & value ) //accept by const reference
{
    m_value = value;
    return *this; //you've to return!
}

Answer 2

You have some of the Ts in the wrong place. It should be

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

This will let you do

Integer a(4);
Float b(6.2f);

a = b;

cout << a.value() << endl;

and it will print 6, a behaviour similar to that of the int and float types you are imitating.