Modern C++: Efficient and Scalable Application Development

How to do it...

To compose unary functions into a higher-order function, you should:

• For composing two functions, provide a function that takes two functions, f and g, as arguments and returns a new function (a lambda) that returns f(g(x)) where x is the argument of the composed function:

        template <typename F, typename G>         auto compose(F&& f, G&& g)         {            return [=](auto x) { return f(g(x)); };         }         auto v = compose(           [](int const n) {return std::to_string(n); },           [](int const n) {return n * n; })(-3); // v = "9"

• For composing a variable number of functions, provide a variadic template overload of the function described previously:

        template <typename F, typename... R>         auto compose(F&& f, R&&... r)         {  return [=](auto x) { return f(compose(r...)(x)); ...