Instantiating class from a string

[sennetta]

This might not be strictly OOP related, but I wasn't sure and I didn't want to clutter the main board with something that might be inappropriate.

 

I would like to create a function which takes a carefully formatted string as a parameter and creates an instance of an object with arguments taken from the string.  The protocol is as follows:

 

"ClassName_arg1_arg2"

 

On being called the function splits the string (using http://uk3.php.net/split ?) and attempts to create an instance of the class ClassName with arguments Arg1 and Arg2, so, upon receiving such a string, the function essentially needs to carry out the following:

 

<?php
$obj = new ClassName("arg1","arg2");
?>

 

Note that more parameters may be added to the initial string, so it may be

 

"ClassName_arg1_arg2_arg3_arg4_arg5"
resulting in
<?php
$obj = new ClassName("arg1","arg2","arg3","arg4","arg5");
?>

 

or even simply

 

"ClassName"
resulting in
<?php
$obj = new ClassName();
?>

.

 

I've had a think and a way I have come up with is getting the function to build the string

 

"$obj = new ClassName(\"arg1\",\"arg2\");"

 

and then get PHP to parse it, and essentially run the code it has just built.

 

Is this even possible in PHP, and if so am I on the right track?

 

Many thanks,

 

Anthony

[emehrkay]

well if you have the strng "ClassName_arg_arg2" and your run it through split or explode, you know that the zero index is the class name and the rest are the arguments. So your code should could build variable variables and pass them to the constructor of that zero index. Does that make sense?

[sennetta]

Ah so I need to use variable variables?  I've heard of these before but have had reason to explore them further.  Many thanks for your reply - I shall look into it and reopen the topic if I get stuck.

 

Cheers for the help.

[sennetta]

I've heard of these before but have had reason to explore them further.

 

I meant:

 

I've heard of these before but have had no reason to explore them further.

[emehrkay]

You can also use func_get_args(); and just pass whatever to the constructor

 

class test{
    public function __construct(){
        echo func_num_args();
    }
}

$class = 'test';
$vars = 'argument';

$instance = new $class($vars);

[sennetta]

Ah nice one.  I shall look into that also.  Cheers dude.

[deadimp]

I've had a think and a way I have come up with is getting the function to build the string

 

"$obj = new ClassName(\"arg1\",\"arg2\");"

 

and then get PHP to parse it, and essentially run the code it has just built.

 

Is this even possible in PHP, and if so am I on the right track?

It is possible to get PHP to parse your string using eval(), but emehrkay's solution is much cleaner, faster, more secure, etc, meaning there's no reason to use this in this circumstance.

[sennetta]

You can also use func_get_args(); and just pass whatever to the constructor

 

class test{
    public function __construct(){
        echo func_num_args();
    }
}

$class = 'test';
$vars = 'argument';

$instance = new $class($vars);

 

Ok so I have the class name stored as a string, and the arguments stored in a separate array, and I have successfully created an instance of the class like so:

private function createClass(){
require_once($this->className.".php");
$this->classInst = new $this->className;
}

How can I pass a varying number of arguments to the constructor of that class?  I think I can do it by creating a method in the class to pass arguments, and then call a "begin" method which will set the class doing its stuff:

 

private function createClass(){
require_once($this->className.".php");
$this->classInst = new $this->className;

foreach ($this->args as $arg){
	$this->classInst->addArg($arg);
}
$this->classInst->begin();
}

but I'd rather not do that: passing them to the constructor would be a lot neater, and means I wouldn't have to subclass anything - I could just use an interface.  What would you do?

 

Many thanks once again.

[sennetta]

 

... but I'd rather not do that: passing them to the constructor would be a lot neater, and means I wouldn't have to subclass anything later on - I could just use an interface.  What would you do?

 

Many thanks once again.

 

Sorry wouldn't let me edit it.

[sennetta]

Blimey they don't like edits here do they!

 

 

... but I'd rather not do that: passing them to the constructor would be a lot neater, and means I wouldn't have to subclass anything later on - I could just use an interface.  What would you do?

 

Many thanks once again.

 

Sorry wouldn't let me edit it.  I meant:

 

 

... but I'd rather not do that: passing them to the constructor would be a lot neater, and means I wouldn't have to subclass anything later on - I could just use an interface and avoid calling parent constructors and having "criteria" (urgh) for writing a new module.  What would you do?

 

Many thanks once again.

[deadimp]

The best solution for this would be something in the Reflection API, more specifically, ReflectionClass::newInstanceArgs().

Just implemented something using this not too long ago.

You'll need PHP 5 for this, though. If you're using PHP 4, I don't know what to say really, other than just try to use eval().

[448191]

<?php
class Foo {

private $bar;
private $meh;

public static function factory($bar, $meh){
	return new self($bar, $meh);
}
public function __construct($bar, $meh){
	$this->bar = $bar;
	$this->meh = $meh;
}
}
$arr = explode('_', 'Foo_bar_meh');
$foo = call_user_func_array(array($arr[0], 'factory'), array($arr[1], $arr[2]));
var_dump($foo);
?>

[sennetta]

<?php
class Foo {

private $bar;
private $meh;

public static function factory($bar, $meh){
	return new self($bar, $meh);
}
public function __construct($bar, $meh){
	$this->bar = $bar;
	$this->meh = $meh;
}
}
$arr = explode('_', 'Foo_bar_meh');
$foo = call_user_func_array(array($arr[0], 'factory'), array($arr[1], $arr[2]));
var_dump($foo);
?>

Thanks very much.  That was exactly what I needed.  Here is the code I wrote.

<?php
private function createClass(){
require_once($this->className.".php");
// create class instance using factory method in class
$this->classInst = call_user_func_array(
		array(
			$this->className,
			'factory'),
		$this->argsArr); // $argsArr is array of arguments created 
				      // when the input string is exploded

}

?>

and it works, by crikey.