Re: Re: perl OO - to use or not to use

[IlyaM]

Procedural code often tends to separate data and the processes applied to that data. OO tends to do the opposite.

Often procedural code is written in pseudo-OO style. I.e when you see a lot of subs with signatures like

sub do1($datastructure1, ..)
sub do2($datastructure1, ..)
sub do3($datastructure1, ..)

sub do4($datastructure2, ..)
sub do5($datastructure2, ..)
sub do6($datastructure2, ..)

It is relatively easily to convert to OO code. You put all subs which work on same data structures in same classes and then you apply various refactorings(like this, this and this) to get more ideomatic OO code.

--
Ilya Martynov, [e-mail]
CTO IPonWEB (UK) Ltd
Quality Perl Programming and Unix Support UK managed @ offshore prices - http://www.iponweb.net
Personal website - http://martynov.org

[BUU]

Wouldn't the example you mentioned be considered OO programming anyways? I mean, it does the exact same thing as 'traditional' OO programming, it just has a slightly different form. Do we have to have a 'class' and then create an 'object' and then call a method on the object by using specialized syntax? Why would this: $obj->meth(); be considered OO and this meth($obj) not be?

[liz]

With OO, the subroutine "meth" could be inherited (exist in another namespace from which the object inherits). When called as a subroutine, the subroutine must exist in the current namespace (or some pretty heavy AUTOLOAD magic should be involved).

Liz

[IlyaM]

Other important difference is that in case of OO syntax caller in general doesn't know how $obj will handle method call (i.e. caller doesn't know which subroutine in which package is going to be called) as it depends on the class of $obj.

--
Ilya Martynov, [e-mail]
CTO IPonWEB (UK) Ltd
Quality Perl Programming and Unix Support UK managed @ offshore prices - http://www.iponweb.net
Personal website - http://martynov.org

[IlyaM]

First of all I'd like to mention that the syntax is secondary to the design of system. It is possible to express OO design using purely procedural syntax (case in point: first C++ compilers were actually just preprocessors which generated C code they feed to real C compilers). And of course it is quite possible to write purely procedural code using OO syntax.

The syntax meth($obj) will work as substitution for $obj->meth() until you need data abstraction (i.e. you don't have classes which share same interfaces, particulary your class tree is flat and you don't use inheritance). Some would argue that data abstraction is essential property of OO design and if a system doesn't use data abstraction it is not OO at all.

--
Ilya Martynov, [e-mail]
CTO IPonWEB (UK) Ltd
Quality Perl Programming and Unix Support UK managed @ offshore prices - http://www.iponweb.net
Personal website - http://martynov.org

[signal9]

Do we have to have a 'class' and then create an 'object' and then call a method on the object by using specialized syntax?

Yes, that is exactly the point of object oriented programming. For it to be OO programming, you need to be able to create multiple instances of a class with all attributes and functions implied by that class.

Your second examples are not analagous. In the case of $obj->meth();, the programmer is calling a method which belongs to the class, or the instance of that class. In the case of meth($obj), the programmer is passing a variable to a function which has no inherent relationship to the variable passed. The examples may look somewhat similar, but they are doing very different things.