Automating dynamic calls with multiple dispatch
Multiple dispatch is an extension of the concept of virtual functions. With a virtual function, the exact function called depends on the runtime type of the this object. With multiple dispatch, the exact function called depends on the runtime type of two or more objects. D does not have support for multiple dispatch built into the language, but with some code generation, we can add it ourselves.
Getting ready
Let's consider how we will do it manually. Given two or more class objects and a list of functions, we will need to call the most specific function possible for their dynamic type.
To determine if a class is more specific than another, we look at the inheritance hierarchy. If class A is a parent or an ancestor of class B, class B is more specific than class A. This makes the generic root class, Object, which has no parents, the least specific of all.
To determine if an object is an instance of a more specific class, we attempt to cast it and...
