In which cases one needs to specify the template's argument `types` specifically?

Question

// Function declaration.
template <typename T1, 
          typename T2, 
          typename RT> RT max (T1 a, T2 b);

// Function call.
max <int,double,double> (4,4.2)

// Function call.
max <int> (4,4.2)

One case may be when you need to specify the return type.

Is there any other situation which requires the argument types to be specified manually?

Answer 1

(1) When there is no argument to the function and still it's a template type, then you may have to specify the arguments explicitly

template<typename T>
void foo ()
{}

Usage:

foo<int>();
foo<A>();

(2) You want to distinguish between value and reference.

template<typename T>
void foo(T obj)
{}

Usage:

int i = 2;
foo(i); // pass by value
foo<int&>(i); // pass by reference

(3) Need another type to be deduced instead of the natural type.

template<typename T>
void foo(T& obj)
{}

Usage:

foo<double>(d);  // otherwise it would have been foo<int>
foo<Base&>(o); // otherwise it would have been foo<Derived&>

(4) Two different argument types are provided for a single template parameter

template<typename T>
void foo(T obj1, T obj2)
{}

Usage:

foo<double>(d,i);  // Deduction finds both double and int for T