Hands-On Design Patterns with C++

Class templates

Class templates are classes that use generic types, usually to declare its data members, but also to declare methods and local variables inside them:

template <typename T>class ArrayOf2 {    public:    T& operator[](size_t i) { return a_[i]; }    const T& operator[](size_t i) const { return a_[i]; }    T sum() const { return a_[0] + a_[1]; }    private:    T a_[2];};

This class is implemented once, and can then be used to define an array of two elements of any type:

ArrayOf2<int> i;i[0] = 1; i[1] = 5;std::cout << i.sum();     // 6ArrayOf2<double> x;x[0] = -3.5; x[1] = 4;std::cout << x.sum();     // 0.5ArrayOf2<char*> c;char s[] = "Hello";c[0] = s; c[1] = s + 2;

Pay particular attention to the last example—you might expect the ArrayOf2 template not ...