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
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
A function object is just that. Something which is both an object and a function. Aside: calling a function object a “functor” is a serious abuse of the term: a different kind of “functors” are a central concept in mathematics, and one that has a direct role in computer science (see “Haskell Functors”). The term … Read more
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
The word “functor” comes from category theory, which is a very general, very abstract branch of mathematics. It has been borrowed by designers of functional languages in at least two different ways. In the ML family of languages, a functor is a module that takes one or more other modules as a parameter. It’s considered … Read more
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
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
I’ve accidently written a Haskell Functors Tutorial I’ll answer your question using examples, and I’ll put the types underneath in comments. Watch out for the pattern in the types. fmap is a generalisation of map Functors are for giving you the fmap function. fmap works like map, so let’s check out map first: map (subtract … Read more
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
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