Templates

Write one function or class that works for many types.

C++

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

template <typename T>
T largest(const vector<T> &items) {
  T best = items[0];
  for (const T &x : items) {
    if (best < x) {
      best = x;
    }
  }
  return best;
}

template <typename T>
class Box {
  T value;

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

int main() {
  cout << largest(vector<int>{3, 9, 4}) << "\n";
  cout << largest(vector<string>{"pear", "apple", "mango"}) << "\n";
  Box<double> b(8.5);
  cout << b.get() << "\n";
  return 0;
}

Output

9
pear
8.5

The compiler writes a separate version of largest for each type you use it with. The type only needs the operations the template uses, here copying and <. Strings compare in dictionary order, so pear is the largest.

vector, map, sort and unique_ptr are all templates. That is why the angle brackets appear everywhere in C++ code.

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