Swedish fika

Overloading constructors in PHP

Jun 6 2008

As far as I know, there is not an easy way to overload a constructor in PHP in the same way as in C# or Java. There seems to be a whole bunch of different solutions or workarounds regarding this issue. I’ve been working a lot with PHP in my degree project and this is the technique we used to “overload” constructors.

You can create an array that contains your arguments and then check which parameters that are set in the array in the constructor. First you check the length of the parameter list and then which parameters that are declared. Then you set the class instance variables to the corresponding parameter value.

class Something { private $a; private function SetA($a) { $this->a = $args['a']; } function __construct($args) { $numArgs = sizeof($args); switch ($numArgs) { case 1: if(isset($args['a'])) { $this->SetA($args['a']); } break; } } }

In whatever file that you need to create an object of the class above you can write the following code:

$args = array('a' => 'someValue'); $s = new Something($args);

The thing that I like the most with this technique with using an array in PHP is that you will most unlikely run out of a possibility to set whatever you want to set in your constructor. When you’re programming with C#, for example, it’s pretty easy to run out of constructors. Have you once declared a constructor that takes one string parameter you cannot overload that constructor with another constructor that also takes one string parameter.

Is there anyone who have another idea/tip on how to overload constructors using PHP?

Comments

woodie Jun 18 2008

this is good stuff:)

keep it up!

Per Jul 22 2008

I prefer to create a construct without any arguments, and then create functions with different arguments. In ASP.NET you can create as many constructs you want, but PHP doesn’t works like that. It’s sad, but this is my opinion

Simon Kjellberg Jul 22 2008

@Per - That’s perhaps the best/easiest way to do it. I think I’ll use that way from now on. I usually like to validate everything when I create an object but you can still validate everything in a function so I guess it’s easier to do it like you do when you’re developing with PHP.

k3n Aug 22 2008

That is one way to do it, althought I also like to use that technique if a method I’m developing requires more than about 3 parameters. It provides lots of flexibility, without the problems that default values, ordering, and readability give you. Cheap named parameters.

You could also use func_get_args(), although I’m not sure how references would be handled, and the code would be less ledgible.

Brian Reich Aug 23 2008

What he said!

I’ve always used func_num_args() and func_get_args() to pull this off. You can use a switch or if/else to call another initialization method based on the number and type of arguments passed.

Having said that, what you mentioned reminds me a lot of the configuration array methodology I see in the Zend Framework. Many class constructors in ZFW allow you to pass either a Zend_Config object or an associative array of options, rather than a long and confusing list of parameters.

You can make this method all the more powerful by creating a “defaults” array and using array_merge() to apply any defaults to the user’s configuration that they didn’t explicitly set.

I’ve adopted this method in my own programming for initialization of any class that requires more than 2 or 3 initialization parameters.

Piccolo Principe Aug 24 2008

Maybe using static factory methods in the class could be the solution, like ::fromAB(), ::fromC() etc.
However the best approach could be define some setters in the class and to create a factory that take care of the instantiation of objects: this avoids mixing creation and business logic in the same class.