phpdesign-patternsmethodsfactory

Is this Factory Method the good one for what I'm trying to do?


Here is what I am trying to achieve:

class Parser
{
    protected $src;
        
    public function __construct($src)
    {
        $this->src = $src;
    }   
}

class Format1Parser extends Parser
{
    public function Parse()
    {
        // Parsing format 1
        // ...
    }
}

class Format2Parser extends Parser
{
    public function Parse()
    {
        // Parsing format 2
        // ...
    }
}

class ParserFactory
{
    public static function GetParser($src)
    {
        $header = substr($src,0,7);
        if ( $header == "format1" )
        {
            return( new Format1Parser($src) );
        }
        if ( $header == "format2" )
        {
            return( new Format2Parser($src) );
        }
        return(false);
    }   
}

$parser = ParserFactory::GetParser( file_get_contents("file.txt") );
$parser->Parse();


Solution

  • First, I would use a suffix (Parser_Format1) instead of a prefix (Format1Parser), because IMHO it's clearer.

    As for the factory method itself, you could use dynamic instantiation:

    class ParserFactory {
       static public function getParser($src) {
          // may want to change the following line, because it assumes your parser
          // type is always 7 characters long.
          $type = substr($src, 0, 7); 
    
          $pattern = 'Parser_%type';
          $className = str_replace('%type', $type, $pattern);
          if (!class_exists($className)) {
             throw new InvalidArgumentException("Invalid parser $type");
    
          return new $className;
       } 
    }
    

    Another thing, your Parser class should be abstract and define an abstract function Parse():

    abstract class Parser {
        protected $src;
    
        public function __construct($src)
        {
            $this->src = $src;
        }   
    
        abstract public function Parse();
    }
    

    Defining abstract methods within a base abstract class ensure that most errors (i.e.: a missing Parse method) are caught when the class is parsed (at the beginning of the program), as opposed as to when it's called (in the middle of runtime).