Class Template Argument Deduction in member variables

Question

Expanded version here.

We can create objects of class templates that have default template parameters without typing angle brackets:

int main()
{
            


        

Answer 1

No, it is not a bug. It is because there could be different constructors called for the same member variable (called through class' constructor init list), potentially yielding different deduction result.

To prevent the potential for such conflict, you have to provide template arguments to non-static members. (Static members are not a problem, because there will a be a single constructor call for them)