Thanks for the link. I looked at it, and while I did not come any closer to solving the riddle of how to code to an interface instead of an implementation in PHP, it’s a very good PHP site. One of the insights that I liked very much is Will Fitch’s observation that the Factory Pattern (I believe he actually meant Factory Method Pattern) can be used instead of the Singleton. I think that may be useful for those who want Singleton functionality but who do not like the Singleton’s problems (see We Don’t Need No Stinkin’ Singletons).

I don’t mean to sound like I’ being a purist (and certainly not a prig!) about OOP and Design Patterns. I want to be as inclusive as possible when it comes to OOP/DP. Rather, I’m looking for a way to use design patterns with PHP. I am convinced that there’s a workaround that serves the same function as typing an object to an interface instead of an implementation in PHP, but I just haven’t found it yet. In the original post I noted Matt Zandstra’s code structure:

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function __construct($propertyA, Strategy $strategy)
{
	$this->propertyA =$propertyA;
	$this->strategyProp = $strategy;
}

Where “Strategy” is an interface in the Strategy pattern. This may be how to program to an interface instead of an implementation in PHP. I’m just not sure though because I’m more of a weekend PHP programmer than a hard core one like many.

So if you can help us out on this key design pattern principle as it applies to PHP, I’d be most grateful. Maybe Matt’s explanation would make more sense to a PHP programmer than to an ActionScript 3.0 one!

Kindest regards,
Bill

You might want to check out http://www.phpfever.com/. They have lots of PHP design pattern postings. It may not be pure enough to meet your formal def, but I think it gets the benefits of design patterns.

Daniel

Thank you for your comment–I’m especially interested in how the PHP folks deal with programming to an interface and not an implementation without using typed variables.

I think you hit the nail on the head in pointing out that you cannot make a non-typed language (such as PHP) do something that it is not intended to do. However, I find lots of PHP design patterns out there, but they all seem to be coding to an implementation and not an interface (abstract class or interface.) Since the first dictum of design patterns by GoF is to program to an interface instead of an implementation, I’m curious how that might be done.

If you know any PHP coders who use design patterns, I’d like to find out how they do that.

Thanks,
Bill

Second, if you do need to check the type of item passed you can accomplish it by putting a check on the setting of the property with the PHP magic getter and setter methods. These are methods called by PHP when you try to access an object’s property outside of the object. For example:

{$key} = $value;
}
?>

I’m sort of a Notepad programmer when it comes to PHP. I’m going to play around with the instanceof check. By the way, if you put in:

< ?php .... and....?> when using the plugin with PHP, you get the color coding:

Like this:

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<?php
function makeSureMyParamsAreGood( MyClass $obj )
{
    // ...
}
?>

Cool, huh?

Cheers,
Bill

Being a dynamically typed language, PHP errors only appear at run-time. Many errors were type mismatches that would be easily caught in a statically typed language during compile-time. “Trying” is the key here as a PHP type error manifests itself somewhere other than where the culprit resides. One has to backtrace the call stack to isolate the type error.

I actually ended up writing a logger plugin that enabled me to pretty print PHP objects onto the browser console just to help with debugging. However, logging variables is a poor substitute for strong typing.

A type check on function parameters would be a big help indeed. I went back to my favorite PHP 5 book – “PHP 5 Power Programming” by Gutmans, Bakken, and Rethans. Lo and behold, PHP 5 does have a built-in type check for function parameters.

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function makeSureMyParamsAreGood( MyClass $obj )
{
    // ...
}

When the above function is called, PHP will do an instanceof check to make sure that the $obj is of type MyClass. If not, it will throw an error. The cool thing is that the instanceof check returns true even if $obj is an instance of a subclass of MyClass.

It would be nice to have a PHP IDE that does type checking. Wonder if Zend Studio does this?

http://www.ericbess.com/ericblog/2008/03/03/wp-codebox/

Great Blog!

Thanks for the tip. I’ve heard about the Zend PHP framework and took a quick look at it. However, I don’t remember seeing instances typed to an interface. Because abstract classes cannot be instantiated, I have not yet solved the riddle of how to program to an interface instead of an implementation in PHP.

Zend PHP sounds like a good place to dig. I’ll start shoveling!

Kindest regards,
Bill