Default argument for type parameters for class template

It is possible to provide default type to the template type for class templates. For example,

#include <iostream>
 
template <typename T = int, typename U = int>
struct Collection
{
    T a{};
    U b{};
};
 
template <typename T, typename U>
void printCollection(Collection<T, U> p)
{
    std::cout << "{" << p.a << ", " << p.b << "}" << "\n";
}
 
int main(int argc, char const *argv[])
{
    Collection c1{1, 2};
    printCollection(c1);
    
    Collection c2;
    printCollection(c2);
    return 0;
}

For c1, CTAD deduces the type as Collection<int,int> and for c2 default types are used which is Collection<int,int>.

References

1. https://www.learncpp.com/cpp-tutorial/class-template-argument-deduction-ctad-and-deduction-guides/