1. A function template is instantiated either (1) when it is invoked or (2) when its address is taken. 
     #include <iostream>
	
 template <typename T>
 void foo(T t){ std::cout << t << std::endl; };
	
 int main(){
    foo(1);
    void (*pf)(int) = &foo;
    pf(2);
    return 0;
 }
  2. When the address of a function template instantiation is taken, the context must be such that it allows a unique type or value to be determined for a template argument. 
     #include <iostream>
	
 template <typename Type, int size>
 Type min(Type (&r_array)[size]) {
     Type m = r_array[0];
     for (int i = 1; i < size; ++i) {
         if (r_array[i] < m)
             m = r_array[i];
     }
     return m;
 }
	
 typedef double (&rad)[3];
	
 void func(int (*f)(int (&)[4])) {
     int arr[4] = {9, 3, 5, -1};
     std::cout << "Minimum int: " << f(arr) << std::endl;
 }
	
 void func(double (*f)(rad)) {
     double arr[3] = {9.1, 3.2, 19.0};
     std::cout << "Minimum double: " << f(arr) << std::endl;
 }
	
 int main() {
     // Error: ambiguous call
     func(&min);
	
     // This call selects the instantiation: double min(double (&)[3]).
     func(static_cast<double(*)(rad)>(&min));
	
     // This call selects the instantiation: int min(int (&)[4]).
     func(static_cast<int(*)(int (&)[4])>(&min));
	
     return 0;
 }