This is just how protocols currently dispatch methods. A protocol witness table (see this WWDC talk for more info) is used in order to dynamically dispatch to implementations of protocol requirements upon being called on a protocol-typed instance. All it is, is really just a listing of the function implementations to call for each requirement … Read more
You can either add a type parameter to your struct, as in Zernike’s answer, or use a trait object. Using the type parameter is better for performance because each value of T will create a specialized copy of the struct, which allows for static dispatch. A trait object uses dynamic dispatch so it lets you … Read more
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 … Read more