Function Templates

A way in C++ to make functions polymorphic

template <typename T> // <...> can also be written <class T>
int compare (const T &value1, const T &value2){
	if (value1 < value2) return -1;
	if (value2 < value1) return 1;
	return 0;
}

int main (int argc, char **argv){
	int main(int argc, char **argv) {
	std::string h("hello"), w("world");
	std::cout << compare(10, 20) << std::endl; // ok
	std::cout << compare(h, w) << std::endl; // ok
	std::cout << compare("Hello", "World") << std::endl; // hm... 
return EXIT_SUCCESS;}
}

The compiler doesn’t generate any code when it sees the template function

• It doesn’t know what code to generate yet, since it doesn’t know what types are involved
• When the compiler sees the function being used, then it understands what types are involved
  • For example: if we use a “double” version and a “string” version of compare, we will create a version of compare for each type.

Pro of template:

Generate pretty efficient code, no penalties using a template.

Examples

This also work

Conventions

Because the main function need to now the whole body of comp, you can not just make the prototype in the .h file.