Implementing multiple dispatch polymorphism

Wed, 15 Mar 2017 20:00:00 +0300

As we saw previously, many popular OOP languages support subtype polymorphism with single dispatch. This means that the dynamic resolution of a polymorphic call happens with respect to one argument only: the this reference.

The problem with this limitation is that it’s completely arbitrary. In a well-written program, there is no natural tendency for polymorphism to be useful only in one dimension. Quite the contrary – if a program is written with best OOP practices in mind (e.g. one responsibility per class), chances are that the need for multidimensional polymorphism, also called multiple dispatch, will eventually arise.

Implementing single dispatch polymorphism

Wed, 15 Mar 2017 20:00:00 +0300

Many object-oriented languages have support for subtype polymorphism with single dispatch over the this argument.

To implement polymorphic calls, they need a way of accessing information about which override should be selected at runtime. At least for compiled languages, the most obvious way to store this information is in the form of function pointers. The structure that contains these function pointers is called a dispatch table.

object-oriented-programming on Mature Pessimizations - A programming blog by Theodoros Chatzigiannakis

Implementing multiple dispatch polymorphism

Implementing single dispatch polymorphism