templates c++

Question

hey guys
i have a noob question about templates. if i define my member function of a class outside of it and i use a template why cant i use any data type i want anymore?
ex:
template <class T>
T Pair<T>::bigger()//bigger is a function which returns the bigger value
main(){
Pair <T> obj(11, 22);// compiler doesnt like it
}

Answer 1

The compiler complains because T is not a valid type, and could not be deduced.

In main, if you are using an older C++ compiler, you need to pass the type of the arguments you are passing to your constructor, or the type you require for use later, in case of a default constructor.

Eg:

Pair<int> ob(3,4);

This is why we use templates in the first place. To substitute the general type T with a type of our preference as per our need.

In a compiler supporting C++17, you no longer need to pass the type in angle brackets, as the compiler can now deduce it for you, using a feature called Class Template Argument Deduction (CTAD).

Eg :

Pair ob(3,4); // ob is a Pair<int>.