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Posted by Toby A Inkster on 05/17/07 09:01
gosha bine wrote:
> In your everyday natural language, how often do you use verbs without
> nouns and nouns without verbs?
Go away! (is an example)
It's not so much a case of using nouns alone, or verbs alone; but OOP
promotes nouns as "masters" and verbs as "slaves". A verb cannot be
invoked without first referencing some noun.
As a practical example, consider this code in PHP:
function dump_obj($o)
{
echo get_class($o) . "\n";
$M = get_class_methods($o);
sort($M);
foreach ($M as $method)
echo "+ {$method}()\n";
$K = get_class_vars($o);
sort($K);
foreach ($K as $key)
{
$val = $o->$key;
if (is_array($val))
$val = sprintf('Array, length %d', count($val));
elseif (is_object($val))
$val = sprintf('Object, type %s', get_class($val));
elseif (is_string($val))
{
if (strlen($val)<40 && !strstr($val, "\n"))
$val = sprintf("'%s'", addslashes($val));
else
$val = sprintf('String, length %d', strlen($val));
}
elseif (is_bool($val))
$val = $val?'TRUE':'FALSE';
elseif (is_null($val))
$val = 'NULL';
elseif (!is_numeric($val))
$val = gettype($val);
echo " $key = $val\n";
}
echo "--\n";
}
This can be used like so:
dump_obj($database);
dump_obj($user);
dump_obj($template);
where $database, $user and $template are objects of some type.
Now, probably the best pure-OO method for doing this would be to give each
object you're likely to want to dump a "dump()" method, so you'd have:
$database->dump();
$user->dump();
$template->dump();
However, that means that you need to re-implement the dump() method for
each class your write. You *may* be able to use inheritance here, but
because most OO languages (Java and PHP included) don't support
multiple-inheritance, if your classes are already inheriting from
some other parent class, then inheritance is probably not possible.
So you create the ObjectDumper class.
If you're dumb, you'll code it like this:
class ObjectDumper
{
public function dump (Object $o)
{ /* as above */ }
}
And you'll need to call it like this:
$dumper = new ObjectDumper;
$dumper->dump($database);
$dumper->dump($user);
$dumper->dump($template);
But if you're smart, you'll use a static method, like this:
class ObjectDumper
{
public function __construct ()
{ throw new Exception('Do not create instance of ObjectDumper.'); }
public static function dump (Object $o)
{ /* as above */ }
}
And then you can just code this:
ObjectDumper::dump($database);
ObjectDumper::dump($user);
ObjectDumper::dump($template);
Some OO purists will contest that the above is somehow "better", but when
asked why, they'll generally fall back on "because it's object-oriented"
as if that were an end in itself.
OO should not be treated as an end in itself. OO is often, some might even
say usually, a good way of modelling complex projects, and classes provide
a good way of organising code, minimising naming collisions and increasing
code legibility.
However, it doesn't always make sense. In the above ObjectDumper example,
the object oriented code is:
1. Bigger: requires more code;
2. Slower: requires more parser time, and in the case of the
"dumb" example, requires time to instantiate the object; and
3. No more readable than the original dump_obj() function.
Java forces you down the object-oriented route every time. PHP (and PHP is
by no means alone in this matter) allows you to use object-oriented methods
when appropriate, and procedural programming when it makes sense.
--
Toby A Inkster BSc (Hons) ARCS
http://tobyinkster.co.uk/
Geek of ~ HTML/SQL/Perl/PHP/Python/Apache/Linux
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