PHP: classes using each other

Question

I have parent class Color and children, ColorRGBA and ColorHSLA. In class Color I want to use a static functions from these children, but I got error "Class 'Color' not found." Here is the same problem http://forums.codeguru.com/showthread.php?t=469995 but class Color; doesn't seem to work in PHP.

Color.php:

include_once 'ColorRGBA.php';
include_once 'ColorHSLA.php';

class Color{
    public static function isValid(&$tokens, $i) {
        return ColorRGBA::isValid($tokens, $i) || ColorHSLA::isValid($tokens, $i);
    }
}

ColorHLSA.php and similarly ColorRGBA.php

include_once 'Color.php';

class ColorRGBA extends Color {
    public static function isValid(&$t, &$i) {
        ...
    }
}

How should I rebuild my class hierarchy or include directives? Or is there any other option how to make my code work?

vstm · Accepted Answer · 2012-06-06 18:10:48Z

2

Yes in PHP there are no "forward declarations" like in C++. That's why class Color; is invalid in PHP.

Now why do you get "Class 'Color' not found."? The problem is that, this line

class ColorRGBA extends Color

gets executed before that line:

class Color {

So Color is indeed not defined. To solve this you could do the following:

class Color{
    public static function isValid(&$tokens, $i) {
        include_once 'ColorRGBA.php';
        include_once 'ColorHSLA.php';
        return ColorRGBA::isValid($tokens, $i) || ColorHSLA::isValid($tokens, $i);
    }
}

This works because the Color class is now fully defined and the ColorRGBA/ColorHSLA classes are defined only when isValid gets called.

You could also put include_once after the definition of the Color class.

answered Jun 6, 2012 at 18:10

vstm

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Comments

afuzzyllama · Accepted Answer · 2012-06-06 18:24:19Z

0

To get around this type of problem, perhaps you should think about implementing a factory class. If that isn't your style, another elegant way around this issue is it use __autoload().

As for the maintenance of the code. It is going to be difficult depending on how many colors you introduce. Why not trying something like:

class Color{
    public static function isValid($type, &$tokens, $i){
        $class_name = 'Color'.$type;            
        if (!class_exists($class_name)) {
            throw new Exception('Missing '.$class_name.' class.');
        }

        $class_name::isValid(&$tokens, $i);
    }
}

PHP 3.5+

edited Jun 6, 2012 at 18:24

answered Jun 6, 2012 at 18:16

afuzzyllama

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3 Comments

user1440369 Over a year ago

It is parser of CSS files, so there is valid only RGBA and HSLA colors unless they present CSS4 standard. You inspired me to create this solution $r = 'ColorRGBA'; $h = 'ColorHSLA'; return $r::isValid($tokens, $i) || $h::isValid($tokens, $i); It works perfectly, thank you.

hakre Over a year ago

@user1440369: There are also named colors in CSS.

user1440369 Over a year ago

I have found only RGB values of named colors in CSS, so I've included this functionality to ColorRGBA class, or should I separate this functionality to another class?

robonerd · Accepted Answer · 2012-06-06 18:07:41Z

0

You cannot include ColorRGBA.php in Color.php and Color.php in ColorRGBA.php. You will get circular dependency. This is why you get class not found error.

answered Jun 6, 2012 at 18:07

robonerd

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2 Comments

user1440369 Over a year ago

When I remove include_once "Color.php" from ColorRGBA.php and ColorHSLA.php, the error is still there. And shouldn't include_once include resource only one time?

robonerd Over a year ago

It's not about including it once. It's about including files in each other. It's called circular dependency. Try removing include Color.php statement from ColorRGBA.php and folowing extends Color statement. You can leave your Color class as is.

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