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Just cuz the O'Reilly examples were crap...
Object-oriented programming in PHP.
As somebody whose background in languages is mostly in C, the whole OOP thing is a bit of a mystery to me. I've yet to work out why an object is better than procedural functions & structs etc., but I'm sure that'll come in time.
But I've got a few O'Reilly books laying around on the subject of PHP, so I looked to them for an answer as to what OOP really *is*
For once, they were useless. Not only because they have bugger all in the way of explanations, but also because they have such godawful code examples.
It's the names they use. One book has the same name for an object as a function, so when they refer to 'Song' you can't tell if they're calling the object or the function IN the object.
The other has the same name for two different variables. So you get this dazzlingly-clear example:
$this->str = $str;
WHICH str is which?? What IDIOT thought this was a good example??
(Actually, I can answer that one - Rasmus Lerdorf, apparently, thought having two variables with the same name would make the example easy to follow)
So I sat down and worked through the creation of an object. There's absolutely nothing useful about the code I came up with, except for the fact that if you've no idea how PHP does OOP things, this'll make things a little bit clearer. So here it is, published online just on the offchance that anyone else wants to know just how the Hell to get started with objects in PHP.
Follow up:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>PHP OOP test</title>
</head>
<body>
<?php
// Define a new object called "object_example"
class object_example {
//Define an object variable
var $object_variable = 'Object-defined variable';
//Define a function that modifies the object variable
function object_variable_rename_function($function_variable) {
$this->object_variable = $function_variable;
}
//Define a function to echo the object variable
function object_echo() {
echo $this->object_variable . '<br />';
}
}
//Right, having defined an object, let's make use of it!
//Create a new instance of the object & echo its default variable
$test_object = new object_example;
$test_object->object_echo();
//Use object's redefine function to change value of its variable
$test_object->object_variable_rename_function('Function-defined variable');
$test_object->object_echo();
//Use 'extends' to create a new object that inherits from our first object
class inheriting_object extends object_example {
function object_variable_length() {
echo 'The default string, <em>"' . $this->object_variable . '",</em> is ' . strlen($this->object_variable) . ' characters long.';
}
}
$test_extended_object = new inheriting_object;
$test_extended_object->object_variable_length();
?>
</body>
</html>
And the output will be (in W3C-compliant code, of course)
Object-defined variable
Function-defined variable
The default string, "Object-defined variable", is 23 characters long.
16 comments
You just have to make some structs. And, uh, functions that operate on the structs.
http://source.winehq.org/source/include/wine/list.h
The important features:
* We have an "object", a list, which represents either a doubly-linked list or an item in a doubly-linked list.
* There are a bunch of functions/macros that operate on these lists, and their names start with list_ or LIST_ so we know they're related.
* They are sufficiently generic that I could use them to make a list of anything, just as long as I make a struct with a list in it and whatever else I want a list item to contain.
* All the functions are in one place. In this case, they're declared statically, but you could also put all the function implementations in a C file and link it to your main program or library t build time.
* When using lists, you write things like list_remove(&item->list) and leave the details of how to remove a list item out of your code.
See also http://en.wikipedia.org/wiki/Object-oriented_programming#Fundamental_concepts_and_features. All of these concepts can be used in C when they are useful, and they often are.
The problem with OOP is that the Java people hyped up the term and turned it into a Silver Bullet that would solve everything. Of course it doesn't.. and it doesn't help that Java is actually a really terrible OOP system. PHP's OOP is terrible too.
Here is that article:
http://www.geocities.com/tablizer/model.htm
I must say it makes a lot of sense to me.
@Vincent - yeah, I know OOP is more down to how you write code than to the language. But C was never intended as an OOP language, so the books on writing it are procedural-based too: Learning C is unlikely to make you an OOP guru!
@Hari - I can see how it could be a good system in some situations, but I can't say I'm really much of a fan of it yet myself either.
@Tuxdev - what makes C++ so much better at OOP for you? (That's a question not an argument - I don't know Java or C++ at all, and I'm only starting to look at PHP's OOP..)
OOP only really start to shine when combined with functional or declarative programming for the actual executable bits.
@oneandoneis2 I mostly really like C++'s static typing. It's a lot easier to know what I can do with a particular object if it's nicely tagged with a type rather than everything being simply a "var". Also, the type for an argument indicates what properties or abilities the function expects from it. What kind of thing am I supposed to pass into object_variable_rename_function? Can't tell just by glancing at the prototype.
http://www.geocities.com/tablizer/oopbad.htm
I think that the author makes some excellent points to debunk common OOP myths. What I like is that he has taken nothing for granted and analyzed every aspect of OOP according to his metrics and showed why he disagrees with the alleged benefits of OOP.
While not a total convert, I must say I have never been an OOP fan in the first place and maybe that article really echoed well with my own (rather nebulous) views.
Doing a little more research on him, he's the same "TopMind" guy that trolled the C2 wiki and got pummeled to the ground by *much* better software developers than myself.
In any case, I hardly begin understand the more technical aspects of the document and no doubt OOP programmers will have plenty of arguments against it.
But that's where I feel OOP fails to deliver. It's relatively easy to "get into" procedural programming. But even after a couple of years of studying OOP related programming in school, I still don't "get" it.
That's where the problem with OOP lies I feel: too much technicalities and too many details of implementation. Also the concepts can take a long time to sink in and turn into useful code from a newbie.
You've probably never actually been taught OO in your classes. You've probably encountered "never use public member data", but that's not OO thinking, just a rule. For some stuff, like coordinates, it makes better OO sense to actually use public members.
OO thinking is a more abstract "what is a clock actually capable of *doing* and what can a clock tell you?". You can set the time, move the time forward, or read the time. That gets us a clock.setTime(), clock.tick(), and clock.toString(). Do you *really* care whether or not it's in memory as unix time-from-1970, or as year/days/hour/minute/second? Does it really make sense to have getters and setters for year/days/..? It might actually make sense to be able to extract years/days/.. individually, but that's an intentional decision, not just because you happened to store the time internally as years/days/..
Another example, from the shorter anti-OOP article, is the relationship between a mugger and the victim. Is it victim.mug(), or mugger.mug(victim)? If you think a little about who is the one actually *doing* something, the answer is obvious.
Going back to coordinates, what do they *do*? You can many of the standard mathematical operations on them, but otherwise it's just a pair or triplet of values *as defined by math, not because it's convenient*.
A lot of the technicalities in "OOP" come from being taught only the (wrong) rules, and not the real concepts.
Nice blog by the way :)
Inheritance, polymorphism and encapsulation are the main things OOP brings to the table. Treating it like a 'silver bullet' is a terrible idea though - overly complicated OOP code is an utter nightmare to debug and only serves to complicate things.
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