How to properly overload the << operator for an ostream?

Question

I am writing a small matrix library in C++ for matrix operations. However my compiler complains, where before it did not. This code was left on a shelf for 6 months and in b

Answer 1

In C++14 you can use the following template to print any object which has a T::print(std::ostream&)const; member.

template
auto operator<<(std::ostream& os, T const & t) -> decltype(t.print(os), os) 
{ 
    t.print(os); 
    return os; 
} 

In C++20 Concepts can be used.

template
concept Printable = requires(std::ostream& os, T const & t) {
    { t.print(os) };
};

template
std::ostream& operator<<(std::ostream& os, const T& t) { 
    t.print(os); 
    return os; 
}