01.08.2007
Method Overloading in PHP5
Although with release of PHP5 we finaly got some long awaited OOP features, sometimes I really miss overloading capability which exists in languages like Java. I am talking about something like this:
class Overloading_Test
{
public void hello()
{
System.out.println("Hello Anonymous");
}
public void hello(String name)
{
System.out.println("Hello " + name);
}
public void hello(String firstName, String lastName)
{
System.out.println("Hello " + firstName + " " + lastName);
}
}
This way you can call either hello with no arguments at all, or with one or two arguments, and proper method would always be called. Unfortunately, if you try something like this in PHP, it would give you fatal error, because basically, methods cannot be redeclared, since support for overloading is not part of core language like in Java.
However, there is still a way to achieve this Java like overloading functionality by using “magic” methods that are described in PHP Manual. Although it is not clear from manual how could you achieve exact functionality like in Java, I played a little bit with __call function, and get interesting workaround.
<?php
class Overloading_Test
{
function __call($method_name, $arguments)
{
//list of supported methods
//only 'hello' for this test
$accepted_methods = array("hello");
//in case of unexistant method we trigger fatal error
if(!in_array($method_name, $accepted_methods))
{
trigger_error("Method <strong>$method_name</strong> doesn't exist", E_USER_ERROR);
}
//we inspect number of arguments
if(count($arguments) == 0)
{
$this->hello1();
}
elseif(count($arguments) == 1)
{
$this->hello2($arguments[0]);
}
elseif(count($arguments) == 2)
{
$this->hello3($arguments[0], $arguments[1]);
}
else
{
return false;
}
}
function hello1()
{
echo "Hello Anonymous<br>";
}
function hello2($name)
{
echo "Hello $name<br>";
}
function hello3($first_name, $last_name)
{
echo "Hello $first_name, $last_name<br>";
}
}
$ot = new Overloading_Test();
$ot->hello();
$ot->hello("John");
$ot->hello("John", "Smith");
//this one will produce fatal error
//$ot->test();
?>
If you run this code, you will get something like:
Hello Anonymous Hello John Hello John, Smith
So, what is going on here? Whenever we call some undeclared method (which is the case with ‘hello’ method here), magic method __call is called, and two arguments (method name and arguments) are passed to it. For this simple test, we only support overloading of ‘hello’ method, so in case you try any other, we trigger fatal error.
What’s going on further is, we simple check number of argumens passed (by counting $arguments array), and call proper method. For the sake of clarity, I only used simple overloading based on number of arguments, but you could also check for argument type (ie string, integer etc.) and call proper method.
So, as you see, method overloading in PHP5 is not as elegant as in Java, but you can still make it. For more information about ‘magic’ fucntions (there are quite a few for member overloading as well), please visit PHP Manual.
You could just do something like this for simplicity –
class SomeClass {
public static function hello( $firstName = false, $lastName = false ) {
if ( $firstName === false && $lastName === false ) {
print(”Hello Anonymous”);
} else if ( $lastName === false ) {
print(”Hello $firstName”);
} else {
print(”Hello $firstName $lastName”);
}
}
}
SomeClass::hello();
SomeClass::hello( “Beef” );
SomeClass::hello( “Mister”, “Beefie” );
Yeah, of corse I could, but then, that wouldn’t be overloading at all, but using default argument values :) Not to mention that you can’t really call the class staticly that way in php 5(SomeClass::hello()) unless class is declared as static, but I guess you just pointed to default arguments solution instead of overloading, without paying attention to that.
Anyway, the whole point of this post is, you can do something simmilar as with my first Java example as easy as you can with Java (at least outside of class).
My main point was that your solution, while it may work, seems more like a workaround than a solution. Granted, my solution is not overloading either, however, to the calling code, it acts the same and is less coding and doesn’t rely on having a string value be correctly typed *G*.. I know as a developer, when I am in code cranking mode I mistype things all the time and since I do use dynamic methods in PHP (see my blog on dynamic getters/setters — Mmm… Beans for PHP) — I know all about using __call() and the power it offers.
To reiterate, I am not saying that your solution is wrong, just that it is not the only way to achieve the effect…
And for the record, the class does not have to be declared static to reference static properties or functions on that class.. *G* I do it all the time.
-cheers-
ok I understand your point, and completely agree that this is more like workaround (or hack) than real solution. Also it could be I picked bad examples with these ‘hello’ stuff since you can achieve the same functionality in less code by using default arguments.
About static … my bad. You *can* call it all the time, although calling non static methods statically produce E_STRICT level warning. Not a big deal, but it is something I am trying to avoid. :)
Very good. I understand how overloading in PHP work from your article. Thanks a lot :)
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How would you do it if you’d wanna call function with the same name and same number of arguments but different types of arguments like this:
MyClass::hello(Word $obj)
MyClass::hello(ExtWord $obj)
this would be a real overloading.