Mark C. Carroll"

A dynamic language is a language in which programs are dynamic entities. In other words, programs can create and change programs.

In C++, the program is basically cast in stone at compile- time. The program cannot create new variables or functions while it's running; variables and functions can only be created in the source code when the program is initially being compiled.

In Dylan, because it's dynamic, the program can create new variables, classes, and methods _while it's running_. You can do things like write a database where the object stored in the database are dylan objects; and create new classes for each type of object that your user creates. In a static language like C++ or Eiffel, you'd have to write a class which implements user defined classes, and rewrite the entire method selection process - but in Dylan, you could just add classes, and used the system built in to the language.

Graham Matthews

Forgive me if I am being stupid but could you not do the same in a functional language? As far as I can see you can so I am not quite sure why the "OO" part of "OODL" is relevant.

Actually, you would need a *dynamic* functional language. At the moment, it is assumed that functional languages are dynamic, but that *could* be compiled away by a (not very) clever compiler. Then you would have lost the ability to "create and change programs," while retaining the properties of a functional program.

Mark C. Carroll"

The object-oriented nature of Dylan and the dynamic nature of dylan are largely orthogonal. The combination of the two is particularly powerful, because of the ability to dynamically create classes. But you are absolutely correct that the fact that Dylan is OO has little to do with the fact that Dylan is dynamic.

Daraius Edibam

It's also more Object-Oriented than C++, because C++ doesn't have real objects ! They exists only in the design- and compilation- phase : after you compiled you object-module, the object is actually 'replaced' with assembler-code (but with the method- definitions still intact). In C++ f.i., you can't just send a 'print' message to an unknown object whose pointer you just found somewhere : you have to known the type in advance ! This situation isn't very flexible for the programmer, which is why (some) people use Objective C, Lisp or Dylan...

David A. Moon

Mr. Carroll's essay was interesting, and certainly one reasonable expansion of the abbreviation "OODL". However, it should be clarified that this is not what Apple means when they say "OODL". Apple's definition can be found