The following code example is taken from the book
C++ Templates - The Complete Guide, 2nd Edition
by David Vandevoorde, Nicolai M. Josuttis, and Douglas Gregor,
Addison-Wesley, 2017
© Copyright David Vandevoorde, Nicolai M. Josuttis, Douglas Gregor 2017
template<typename T, typename A1, typename A2>
class A_Subscript {
public:
// constructor initializes references to operands
A_Subscript (A1 const& a, A2 const& b)
: a1(a), a2(b) {
}
// process subscription when value requested
decltype(auto) operator[] (std::size_t idx) const {
return a1[a2[idx]];
}
T& operator[] (std::size_t idx) {
return a1[a2[idx]];
}
// size is size of inner array
std::size_t size() const {
return a2.size();
}
private:
A1 const& a1; // reference to first operand
A2 const& a2; // reference to second operand
};