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Posted by Chung Leong on 07/07/06 21:06
Mladen Gogala wrote:
> Chung, you're one of my favorite PHP masters and I learned few things from
> you on this group, but the work you're doing has already been done. PHP
> runkit extension, by Sara Golemon, has this possibility:
>
> RUNKIT_IMPORT_OVERRIDE (integer)
>
> runkit_import() flag indicating that if any of the imported functions,
> methods, constants, or properties already exist, they should be
> replaced with the new definitions. If this flag is not set, then any
> imported definitions which already exist will be discarded.
>
> This sounds very much like overloading to me.
No, actually it's not even close. The runkit just exposes
functionalities in the Zend engine. Overwriting a function is not the
same as overloading it. Wikipedia has a good explanation
http://en.wikipedia.org/wiki/Function_overloading.
What Polar supports is a type of dynamic dispatch, controlled by the
types of the arguments. I call it Sematic Polymorphism. It's similiar
to polymorphism in OOP, except functions are bound to meanings not
objects.
Say we have the following functions:
<?
function SaveObjectToDatabase($object:Object, $db:MysqlDB) {
}
function SaveObjectToDatabase($article:Article, $db:MysqlDB) {
}
?>
Both functions are bound to the meaning of "saving an object to a MySQL
database." The second function is bound to a more specific meaning,
that of "saving an object of the class Article to a MySQL database." In
OOP terms we would say that the second meaning is a descendant of the
first. The relationship isn't stated explicitly, but it's understood.
It's neat idea. There're also a host of other features which I think
are pretty interesting. Pragmas for example. Or Flex case identifiers.
If you have time, take a look at the demo program. You can download it
here:
http://sourceforge.net/project/showfiles.php?group_id=171247
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