Template Deduction Based on Function Return Type in C

In C , it can be desirable to utilize template deduction to simplify code that instantiates generic functions based on the data types of the function's arguments. Consider the following example:

GCPtr ptr1 = GC::Allocate();
GCPtr ptr2 = GC::Allocate();

Instead of specifying the generic type parameters explicitly, the goal is to achieve this deduction using the return type of the GC::Allocate() function. However, C does not allow type deduction based on the return type.

class GC
{
public:
    template
    static GCPtr Allocate();
};

Despite the return type being generic, the compiler requires the explicit specification of the template type parameters and when instantiating the GC::Allocate() function.

To mitigate this limitation, an auxiliary function can be introduced:

template 
void Allocate(GCPtr& p) {
    p = GC::Allocate();
}

Using this function, the original goal can be achieved as follows:

GCPtr p;
Allocate(p);

Whether this syntax offers any significant advantage over the explicit type specification is subjective.

Note: In C 11, it is possible to omit one of the type declarations using the auto keyword:

auto p = GC::Allocate(); // p is of type GCPtr