Why does a js map on an array modify the original array?

You’re not modifying your original array. You’re modifying the objects in the array. If you want to avoid mutating the objects in your array, you can use Object.assign to create a new object with the original’s properties plus any changes you need: const freeProduct = function(products) { return products.map(x => { return Object.assign({}, x, { … Read more

F# changes to OCaml [closed]

This question has been answered for some time now, but I was quite surprised that most of the answers say what OCaml features are missing in F# – this is definitely good to know if you want to port existing OCaml programs to F# (which is probably the motivation of most of the referenced articles). … Read more

passing functor as function pointer

You cannot directly pass a pointer to a C++ functor object as a function pointer to C code (or even to C++ code). Additionally, to portably pass a callback to C code it needs to be at least declared as an extern “C” non-member function. At least, because some APIs require specific function call conventions … Read more

Why are Promises Monads?

UDATE. See this new library providing functor and monad operators for plain callback-based functions that do not have the issues with theneables: https://github.com/dmitriz/cpsfy The JS Promise is neither a Functor nor an Applicative nor a Monad It is not a functor, because the composition preservation law (sending compositions of functions to compositions of their images) … Read more

Why can’t I define a function inside another function?

It is not obvious why one is not allowed; nested functions were proposed a long time ago in N0295 which says: We discuss the introduction of nested functions into C++. Nested functions are well understood and their introduction requires little effort from either compiler vendors, programmers, or the committee. Nested functions offer significant advantages, […] … Read more

Why use functors over functions?

At least four good reasons: Separation of concerns In your particular example, the functor-based approach has the advantage of separating the iteration logic from the average-calculation logic. So you can use your functor in other situations (think about all the other algorithms in the STL), and you can use other functors with for_each. Parameterisation You … Read more

How do I get the argument types of a function pointer in a variadic template class?

You can write function_traits class as shown below, to discover the argument types, return type, and number of arguments: template<typename T> struct function_traits; template<typename R, typename …Args> struct function_traits<std::function<R(Args…)>> { static const size_t nargs = sizeof…(Args); typedef R result_type; template <size_t i> struct arg { typedef typename std::tuple_element<i, std::tuple<Args…>>::type type; }; }; Test code: struct … Read more