从PHP中的抽象父类访问子方法

Question

I am working on a very simple template engine that would allow others to extend the template parsing functionality via subclassing the TemplateParser class. The skeleton of my TemplateParser class looks like this:

abstract class TemplateParser {

    public static function parse_template($template_file) {
        //Do stuff with $template_file

        $specials = array();
        foreach (get_class_methods(__CLASS__) as $method) {
            if(strpos($method, "replace_") !== false) {
                $specials[] = $method;
            }
        }
    }

}

What I would like to do is be able to take a child class and add any number of replace_XXXXX methods in the child class that the parent "automatically" knows about. My problem is that the __CLASS__ constant is always equal to 'TemplateParser', even when called on a child class. Is there any way that I can get the methods of the child class from within TemplateParser?

Answer 1

If you're going to use a static method why even bother asking users to extend the parent class?

OOP vs. COP

First, what you're suggesting is not OOP -- it's COP (Class Oriented Programming). I'd advise you to consider exactly why you've made TemplateParser::parse_template static in the first place. Is there a really, really good reason ( hint : not likely)? Just because PHP 5.3 introduced late-static binding doesn't mean you should use it willy-nilly all over the place. In fact, static is rarely the best option .

Composition Over Inheritance

Second, your stated use-case doesn't provide any compelling reason for using inheritance. You should almost always favor composition over inheritance. Consider:

interface ParserInterface
{
    public function parse_template($template_file);
}

interface ReplacerInterface
{
    // fill in your own interface requirements here
}

class Parser implements ParserInterface
{
    private $replacer;

    public function __construct(ReplacerInterface $replacer)
    {
        $this->replacer = $replacer;
    }

    public function parse_template($template_file)
    {
        $specials = array_filter(function($method) {
            return strpos($method, "replace_") === 0;
        }, get_class_methods($this->replacer));

        foreach ($specials as $method) {
            $this->replacer->$method($template_file);
        }
    }
}

In the above code we're able to reap all the advantages of Dependency Injection ^wiki and our code is imminently more testable, maintainable and less prone to breakage than had we used a convoluted class-oriented implementation with static .

Answer 2

Late static binding made this possible since php 5.3 with the builtin functions: get_called_class() and/or forward_static_call(). http://php.net/manual/en/language.oop5.late-static-bindings.php

Quick example:

class parent_class {
    public function method() {
        echo get_called_class(),PHP_EOL;
    }
    public static function smethod() {
        echo get_called_class(), PHP_EOL;
    }
}

class child_class extends parent_class {
}

$a = new child_class();
$a->method();
$a::smethod();

This outputs: child_class child_class

Using the newly found class name keep the same logic you had in mind with get_class_methods().

Cheers

Answer 3

Try this:

// Array to hold special functions
$specials = array();

// Get all defined classes in script
$all_classes = get_declared_classes();    

// Loop through all classes
foreach($all_classes as $class)
{
   // Check if class is a child of TemplateParser
   if( is_subclass_of($class,'TemplateParser') )
   {
      // This class is a child of TemplateParser.
      // Get it's methods. 
      foreach (get_class_methods($class) as $method) 
      {
         if(strpos($method, "replace_") !== false) {
            $specials[] = $method;
         }
      }
   }
}

I just wrote that up (with a little referencing of PHP documentation) but haven't tested it. I'm sure you can make it do what you need it to do.