Templates

template <typename T> lets a function work with a type decided at the call site, not when it's written. Unlike Rust's trait-bounded generics, a C++ template is duck-typed: the compiler just needs the operations you actually use inside the function body (here, > and copying) to be valid for whatever T turns out to be.

#include <iostream>
using namespace std;

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

int main() {
    cout << maxOf(3, 7) << endl;
    cout << maxOf(2.5, 1.5) << endl;
    return 0;
}

7
2.5

Class templates

A class can be templated too — Box<T> below works for any type T, with the specific type filled in wherever the class is used, such as Box<int> or Box<string>.

#include <iostream>
#include <string>
using namespace std;

template <typename T>
class Box {
private:
    T value;

public:
    Box(T v) : value(v) {}
    T getValue() const {
        return value;
    }
};

int main() {
    Box<int> intBox(42);
    Box<string> strBox("hello");
    cout << intBox.getValue() << endl;
    cout << strBox.getValue() << endl;
    return 0;
}

42
hello

Next: STL containers and iterators — std::map, std::set, and iterating any container the same way.