Re: Properly handling multiple constructors.

Robert Cummings wrote:

Richard Quadling wrote:

Hi. I have a scenario where I would _like_ to have multiple constructors for a class. Each constructor has a greater number of parameters than the previous one. e.g. <?php class myClass { __construct(string $Key) // use key to get the complex details. __construct(string $Part1, string $Part2, string $Part3) // Alternative route to the complex details. __construct(array $Complex) // All the details } Essentially, SimpleKey is a key to a set of predefined rules. Part1, 2 and 3 are the main details and well documented defaults for the rest of the rules. Complex is all the rules. Each constructor will end up with all the parts being known ($Key, $Part1, $Part2, $Part3, $Complex). But, PHP doesn't support multiple constructors. Initially I thought about this ... __construct($Key_Part1_Complex, $Part2=Null, $Part3=Null) But then documenting the first param as being 1 of three different meanings is pretty much a no go. So I'm looking for a clean and easily understood way to provide this. I won't be the only user of the code and not everyone has the same knowledge level, hence a mechanism that is easily documentable. I think I may need a factory with multiple methods (FactoryKey, FactoryPart1To3, FactoryComplex). Make the factory a static/singleton. All these methods eventually call the real class with the complex rule. Is that obvious enough?

Factory method is probably the cleanest and simplest solution. Just pass an ID as the first parameter to the real constructor and then it can route to the appropriate behaviour:

Here's a better example (tested): <?php class Foo {

    const CONSTRUCT_BLAH = 1;
    const CONSTRUCT_BLEH = 2;
    const CONSTRUCT_BLUH = 3;

    function __construct( $constructId )
    {
        static $map = array
        (
            self::CONSTRUCT_BLAH => '__construct_blah',
            self::CONSTRUCT_BLEH => '__construct_bleh',
            self::CONSTRUCT_BLUH => '__construct_bluh',
        );

        $obj = null;

        if( isset( $map[$constructId] ) )
        {
            $args = func_get_args();
            $args = array_shift( $args );

            call_user_func_array(
                array( 'self', $map[$constructId] ), $args );
        }
        else
        {
            // Generate an error or exception.
        }
    }

    static function __construct_bleh( $arg1 )
    {
        echo "Called: ".__FUNCTION__."( $arg1 )\n";
    }

    static function __construct_blah( $arg1 )
    {
        echo "Called: ".__FUNCTION__."( $arg1 )\n";
    }

    static function __construct_bluh( $arg1 )
    {
        echo "Called: ".__FUNCTION__."( $arg1 )\n";
    }

    static function getBlah( $arg1 )
    {
        return new Foo( self::CONSTRUCT_BLAH, $arg1 );
    }

    static function getBleh( $arg1 )
    {
        return new Foo( self::CONSTRUCT_BLEH, $arg1 );
    }

    static function getBluh( $arg1 )
    {
        return new Foo( self::CONSTRUCT_BLUH, $arg1 );
    }

} $obj = Foo::getBlah( 'blah' ); $obj = Foo::getBleh( 'bleh' ); $obj = Foo::getBluh( 'bluh' ); ?> Cheers, Rob. -- http://www.interjinn.com Application and Templating Framework for PHP