Dynamic Class Construction

axon

I would like to write a function that dynamically creates new objects given only a class name and a list of constructor arguments. At the moment the function uses eval() but I would like to avoid doing this because of the memory footprint it leaves:

	function get_instance_of( $class ) {
		$object = NULL;
		$args = func_get_args();
		$num_args = func_num_args();
		$toeval = "\$object =& new $class( ";
		for( $i = 1 ; $i < ( $num_args - 1 ) ; $i++ ) 
			$toeval = $toeval . "\$args[$i] , ";
		if( $i < func_num_args() ) $toeval = $toeval . "\$args[$i]";
		$toeval = $toeval . " );";
		eval( $toeval );
		assert( $object != NULL );
		return $object;
	}

Is there anyway to call the new operator dynamically and pass it an array of parameters so that it then calls the appropriate constructor or is this impossible?

ednark

$class = 'Foo'
$instance = new $class( 'param1', 'param'2 );

this is valid without an eval
so it should do just what you want without any extra magic

tomhath

I assume you are getting the class name and argument list at runtime (from user input, db, or whatever).

In that case ednark's suggestion only covers half the problem (dynamic class name, but still a fixed argument list).

I think combining ednark's technique with your own suggestion buried in your question would work. Define every class with a single arguement that is an array. Create the object like this (I have no clue if this will actually work, but it should!):

$class = 'Foo'
$instance = new $class( func_num_args());

tomhath

Get args, not num agrs:

$class = 'Foo'
$instance = new $class( func_get_args());

axon

Thanks guys but passing an array to the constructor is not really want I'm looking for: I want the code to be generic enough to be used with any class. It seems that it is impossble to generically call a class constructor with some undefined number of arguments without calling eval, unless I could call call_user_func. But what would be the syntax for such a call and how would I use the new operator?

ednark

why not just leave the construcor empty... although its faux pau to do so, you could just hand set the varibales yourself directly

instead of

$inst = new $class( $foo, $bar, $baz )

you could use this horrible abuse of php

$class = 'ClassFoo';
switch ( $class ) {
    case 'classfoo':
        $vars = array( 'var1'=>'val1', 'var2'=>'val2' )
    default:
        $vars = array();
}

$inst = new $class();
foreach ( $vars as $var=$value ) {
    $inst->$var = $val;
}

blockage

Mabey something like this? Pass in the object properties as an array.

function &instantiate($class, $properties = FALSE)
{
   switch ($properties){
      case TRUE: return new $class(extract($properties));
      case FALSE: return new $class;
   }
}

Let us know if it works.

axon

Unforunately, extract didn't work in this case. I can see what you are trying here but all that happens is you pass the integer return from the function to your constructor.