[erlang-questions] Re: OOP in Erlang

[黃耀賢 (Yau-Hsien Huang)]

On Wed, Aug 11, 2010 at 9:20 PM, Steve Davis <steven.charles.davis@REDACTED
> wrote:

> things going on
> here:
> 1) Data structures and
> 2) Transformations of data structures.
>
>
I agree. Mandatory features of OOP includes encapsulation, abstraction,
inheritance, and polymorphism. After reviewing this thread, opinions are
summarized that including
    * if we do OOP in Erlang syntax,
    * if features of OOP are able to be implemented in Erlang,
    * and if exactly Erlang is an OOP language or OO language.

Now knowledge of OOP is mixture of origin concepts, languages such as
Smalltalk or Java, and UML modelling methods. Recently I read the book
"Design Patterns Explained," which hints that OOP/OOD is to treat
everything,
including primitive datatypes, as object. And he explained how abstraction
is
different from implementation. Then I thought that Erlang treats everything
as
function or process, but really? And, Erlang is not toward OOP, so it may
not
be OOP-like.

Let's consider how to implement OOP in Erlang, either using Erlang syntax
or realizing OOP system in Erlang.

Encapsulation: values and functions should be organized as an object
structure tagged as an object name, belong to some class. It is done by
Erlang record syntax or as a module, and somehow messages are sent
to the object or to some member of the structure. Functions in a structure
may call other fields or functions in other structures. Encapsulation means
how an object is structured. Any object is generated by following a object
specification, the class. Object and class are implemented in the same
way: structure.

Abstraction: it's separated from implementation. Abstraction is done in
Erlang
by hot code replacement.

Inheritance: it should be done by taking objects by following
both superclass
and subclass specifications and then overriding the superclass object with
the subclass object, that is to merge base functions into extended functions
effectively. Inheritance shall not be as copying of superclass object, but
keeping a newest copy of a extended function while keeping the reference to
its base function. Inheritance semantics shall be consistent.

Polymorphism: it means that different objects, even if they are in the same
class, may behave separately. It's not a problem because Erlang has this
feature.

On real OOP, I think that OOP is a feature, and somehow it's the problem
itself.
So, when talking about OOP in Erlang, you can have a try to write Erlang in
OOP style, however, Erlang need not be too OOP-like.