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// 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?
793
A template argument for a template template parameter is the name of a class template. When the compiler tries to find a template to match the template template argument, it only considers primary class templates. (A primary template is the template that is being specialized.)
A template parameter is a special kind of parameter that can be used to pass a type as argument: just like regular function parameters can be used to pass values to a function, template parameters allow to pass also types to a function.
You cannot give default arguments to the same template parameters in different declarations in the same scope. The compiler will not allow the following example: template<class T = char> class X; template<class T = char> class X { };
(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
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