Function Templates

A template is written once and works with any type, substituted in by the compiler at the point it's actually used — C++'s equivalent of Java's generics, resolved entirely at compile time with zero runtime overhead.

template<typename T>
T max(T a, T b) {
    return a > b ? a : b;
}

std::cout << max(3, 7) << std::endl;         // 7 — T is int
std::cout << max(3.5, 2.1) << std::endl;     // 3.5 — T is double
std::cout << max<std::string>("a", "b") << std::endl; // explicit T

Each distinct type used with a template causes the compiler to generate a separate, fully-specialized version of the function behind the scenes — this is why templates carry no runtime cost, at the expense of a larger compiled binary and longer compile times.

Practice

Write a function template T sum(T a, T b, T c) that adds three values of the same type.

template<typename T>
T sum(T a, T b, T c) {
    return a + b + c;
}