为什么不在PHP中使用'protected'或'private'？

Question

I've been working with the Joomla framework and I have noticed that they use a convention to designate private or protected methods (they put an underscore " _ " in front of the method name), but they do not explicitly declare any methods public , private , or protected . Why is this? Does it have to do with portability? Are the public , private , or protected keywords not available in older versions of PHP?

Answer 1

public, private and protected are PHP5 keywords. unfortunately, PHP4 still has a very high install base (especially amongst shared hosting services).

here's a pretty pic showing july usage rates (text in french). spoiler : php4 still has over a 35% usage rate sadly.

Answer 2

There's some good arguments for not using private methods and properties over here: http://aperiplus.sourceforge.net/visibility.php

Includes: makes coding and reading code harder. Makes re-using classes and debugging harder.

I'm not sold either way, but I would like to see an informed rebuttal of that article, if one exists.

Answer 3

PHP5 introduced some hefty changes in the object model. Among supporting visibility, there are various other changes. Be sure to check out:

PHP 4 classes and objects

PHP 5 classes and objects