dynamic-dispatch

Programs written in, for example, Java rely a lot on dynamic dispatch. How are such programs expressed in functional languages such as Haskell? In other words, what is the Haskell way of expressing the idea underneath "dynamic dispatch"? glaebhoerl The answer is deceptively simple: higher-order functions. An object with virtual methods in an OO language is nothing more than a glorified record of functions together with some local state. In Haskell you can use records of functions directly, and store the local state in their closures. More concretely, an OO object consists of: A pointer (vptr)

Coming form a C++/Java/C# background I was expecting to see virtual methods in Swift, however reading the swift documentation I see no mention of virtual methods. What am I missing? Unlike C++, it is not necessary to designate that a method is virtual in Swift. The compiler will work out which of the following to use: (the performance metrics of course depend on hardware) Inline the method : 0 ns Static dispatch: < 1.1ns Virtual dispatch 1.1ns (like Java, C# or C++ when designated). Dynamic Dispatch 4.9ns (like Objective-C). Objective-C of course always uses the latter. The 4.9ns overhead is

s->duplicate() returns an object of type Box* , but I'm getting an error initializing it with Box* . It looks like it's being converted back to Shape* . What is the point of having covariant return types if it's converted back to the base class pointer?: struct Shape { virtual Shape* duplicate() { return new Shape; } }; struct Box : Shape { virtual Box* duplicate() { return new Box; } }; int main() { Shape* s = new Box; Box* b = s->duplicate(); } Error: main.cpp:22:12: error: cannot initialize a variable of type 'Box *' with an rvalue of type 'Shape *' Box* b = s->duplicate(); ^ ~~~~~~~~~~~~~~