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User Contributed Notes
Classes and Objects
midir
02-Mar-2009 03:40
There are a couple of tricks you can do with PHP's classes that programmers from C++, etc., will find very peculiar, but which can be useful.

You can create instances of classes without knowing the class name in advance, when it's in a variable:

<?php

$type = 'cc';
 $obj = new $type; // outputs "hi!"

 class cc {
    function __construct() {
        echo 'hi!';
    }
}

 ?>

You can also conditionally define them by wrapping them in if/else blocks etc, like so:

<?php

 if (expr) {
    class cc {
        // version 1
    }
} else {
    class cc {
        // version 2
    }
}

 ?>

It makes up for PHP's lack of preprocessor directives. The caveat is that the if/else code body must have been executed before you can use the class, so you need to pay attention to the order of the code, and not use things before they're defined.
redrik at gmail dot com
31-Dec-2008 09:08
Maybe someone will find these classes, which simulate enumeration, useful.
<?php
 class Enum {
    protected $self = array();
    public function __construct( /*...*/ ) {
        $args = func_get_args();
        for( $i=0, $n=count($args); $i<$n; $i++ )
            $this->add($args[$i]);
    }
   
    public function __get( /*string*/ $name = null ) {
        return $this->self[$name];
    }
   
    public function add( /*string*/ $name = null, /*int*/ $enum = null ) {
        if( isset($enum) )
            $this->self[$name] = $enum;
        else
            $this->self[$name] = end($this->self) + 1;
    }
}

class DefinedEnum extends Enum {
    public function __construct( /*array*/ $itms ) {
        foreach( $itms as $name => $enum )
            $this->add($name, $enum);
    }
}

class FlagsEnum extends Enum {
    public function __construct( /*...*/ ) {
        $args = func_get_args();
        for( $i=0, $n=count($args), $f=0x1; $i<$n; $i++, $f *= 0x2 )
            $this->add($args[$i], $f);
    }
}
 ?>
 Example usage:
<?php
$eFruits = new Enum("APPLE", "ORANGE", "PEACH");
echo $eFruits->APPLE . ",";
echo $eFruits->ORANGE . ",";
echo $eFruits->PEACH . "\n";

 $eBeers = new DefinedEnum("GUINESS" => 25, "MIRROR_POND" => 49);
echo $eBeers->GUINESS . ",";
echo $eBeers->MIRROR_POND . "\n";

 $eFlags = new FlagsEnum("HAS_ADMIN", "HAS_SUPER", "HAS_POWER", "HAS_GUEST");
echo $eFlags->HAS_ADMIN . ",";
echo $eFlags->HAS_SUPER . ",";
echo $eFlags->HAS_POWER . ",";
echo $eFlags->HAS_GUEST . "\n";
 ?>
 Will output:
1, 2, 3
25, 49
1,2,4,8 (or 1, 10, 100, 1000 in binary)
Jeffrey
08-Oct-2008 06:51
Why should anyone learn what classes and objects are? The short answer is to clarify and simplify code. Take this regular script:

<?php
$item_name = 'Widget 22';
 $item_price = 4.90;
 $item_qty = 2;
 $item_total = ($item_price * $item_qty);
echo "You ordered $item_qty $item_name @ \$$item_price for a total of: \$$item_total.";
 ?>

You ordered 2 Widget 22 @ $4.9 for a total of: $9.8.

You can see clearly that you have to "define and set" the data, "perform a calculation", and explicitly "write" the results - for a total of 5 written statements. But the more you look at it, the more it needs fixin'. If you attempt to do that, your code can get really ugly, really fast - and remember, this is just a simple script! Here's the same program in OOP with all the fixin's:

<?php
 class Item {
  protected $name, $price, $qty, $total;

  public function __construct($iName, $iPrice, $iQty) {
    $this->name = $iName;
    $this->price = $iPrice;
    $this->qty = $iQty;
    $this->calculate();
  }

  protected function calculate() {
    $this->price = number_format($this->price, 2);
    $this->total = number_format(($this->price * $this->qty), 2);
  }

  public function __toString() {
    return "You ordered ($this->qty) '$this->name'" . ($this->qty == 1 ? "" : "s") .
    " at \$$this->price, for a total of: \$$this->total.";
  }
}

echo (new Item("Widget 22", 4.90, 2));
 ?>

You ordered (2) 'Widget 22's at $4.90, for a total of: $9.80.

By loading class Item (which houses all the improvements we made over the first script) into PHP first, we went from having to write 5 statements in the first script, to writing only 1 statement "echo new Item" in the second.
Jason
08-Jul-2008 05:34
For real quick and dirty one-liner anonymous objects, just cast an associative array:

<?php

$obj = (object) array('foo' => 'bar', 'property' => 'value');

echo $obj->foo; // prints 'bar'
 echo $obj->property; // prints 'value'

 ?>

... no need to create a new class or function to accomplish it.
ranema at ubuntu dot polarhome dot com
30-Mar-2008 03:49
Sometimes you just forget to close handles, links, etc and sometimes you are just lazy to do that. PHP 5 OOP can do it automatically by using destructors:

<?php
 class MySqlDriver {
   private $_Link;

   public function __construct( <...> ) {
      $this->_Link = mysql_connect( <...> );
   }

   // this will be called automatically at the end of scope
   public function __destruct() {
      mysql_close( $this->_Link );
   }
}

 $_gLink = new MySqlDriver( <...> );
 // and you don't need to close the link manually
 ?>
osculabond at gmail dot com
07-Oct-2006 06:20
A better way to simulate an enum in php5:

<?php
 final class Days {
    const Sunday     = 0x00000001;
    const Monday     = 0x00000010;
    const Tuesday    = 0x00000100;
    const Wednesday = 0x00001000;
    const Thursday  = 0x00010000;
    const Friday    = 0x00100000;
    const Saturday  = 0x01000000;
    const Unknown    = 0x00000000;

    // ensures that this class acts like an enum
    // and that it cannot be instantiated
    private function __construct(){}
}
 ?>

This will allow you to do things like:

<?php
$day_to_email = Days::Thursday;

if($day_to_email == Days::Wednesday) echo "Wednesday<br />";
if($day_to_email == Days::Thursday) echo "Thursday<br />";
if($day_to_email == Days::Friday) echo "Friday<br />";
 ?>

Which would output:
Thursday

Or if you wanted to get a little fancier you could also do the following:

<?php
$days_to_email = Days::Monday | Days::Wednesday | Days::Friday;

if($days_to_email & Days::Monday) echo "Monday<br />";
if($days_to_email & Days::Tuesday) echo "Tuesday<br />";
if($days_to_email & Days::Wednesday) echo "Wednesday<br />";
if($days_to_email & Days::Thursday) echo "Thursday<br />";
if($days_to_email & Days::Friday) echo "Friday<br />";
 ?>

Which would output:
Monday
Wednesday
Friday
Sï¿_b.
27-May-2005 04:50
We can't create easily anonymous objects like in JavaScript.
JS example :

    var o = {
        aProperty : "value",
        anotherProperty : [ "element 1", "element 2" ] } ;
    alert(o.anotherProperty[1]) ; // "element 2"

So I have created a class Object :

<?php
    class Object {
        function __construct( ) {
            $n = func_num_args( ) ;
            for ( $i = 0 ; $i < $n ; $i += 2 ) {
                $this->{func_get_arg($i)} = func_get_arg($i + 1) ;
            }
        }
    }

    $o = new Object(
        'aProperty', 'value',
        'anotherProperty', array('element 1', 'element 2')) ;
    echo $o->anotherProperty[1] ; // "element 2"
 ?>

You must feel free to make it better :)
28-Mar-2005 11:21
There are 3 simple, and utterly annoying problems with your classes (not because of how you want them to work, but because how the Zend II engine handles them):

1) You cannot type hint string or int/integer in a method signature. This is incredibly annoying that the Zend II engine doesn't support it, but there are workarounds.
2) Supplying null in a method signature for a default value means that you will not accept any null value for that parameter. (therefore the method doesn't need to check if the parameters are null anyway).
3) Sadly, overriding methods is only possible with the Zend II engine via Inheritance or Polymorphism, ( and __construct() can only be defined within a class). If you want to override a method in the same class, my suggestion is to provide the method signature with a $flag = null variable, which you call a SWITCH on to pick what the data should do.

==============================================
Other than the afformentioned, the Zend II engine works very similarly to Java, which has made PHP much more versatile and robust in version 5. Thank you again Zend!
spam at afoyi dot com
21-Mar-2005 01:18
You can call a function defined in an inherited class from the parent class. This works in both PHP 4.3.6 and 5.0.0:

<?php

 class p {
   
    function p() {
        print "Parent's constructor\n";
    }
   
    function p_test() {
        print "p_test()\n";
        $this->c_test();
    }
}

class c extends p {
   
    function c() {
        print "Child's constructor\n";
        parent::p();
    }
   
    function c_test() {
        print "c_test()\n";
    }
}

 $obj = new c;
 $obj->p_test();

 ?>

Outputs:

Child's constructor
Parent's constructor
p_test()
c_test()
farzan at ifarzan dot com
05-Oct-2004 11:04
PHP 5 is very very flexible in accessing member variables and member functions. These access methods maybe look unusual and unnecessary at first glance; but they are very useful sometimes; specially when you work with SimpleXML classes and objects. I have posted a similar comment in SimpleXML function reference section, but this one is more comprehensive.

I use the following class as reference for all examples:

<?php
 class Foo {
    public $aMemberVar = 'aMemberVar Member Variable';
    public $aFuncName = 'aMemberFunc';
   
   
    function aMemberFunc() {
        print 'Inside `aMemberFunc()`';
    }
}

 $foo = new Foo;
 ?>

You can access member variables in an object using another variable as name:

<?php
$element = 'aMemberVar';
print $foo->$element; // prints "aMemberVar Member Variable"
 ?>

or use functions:

<?php
 function getVarName()
{ return 'aMemberVar'; }

print $foo->{getVarName()}; // prints "aMemberVar Member Variable"
 ?>

Important Note: You must surround function name with { and } or PHP would think you are calling a member function of object "foo".

you can use a constant or literal as well:

<?php
define(MY_CONSTANT, 'aMemberVar');
print $foo->{MY_CONSTANT}; // Prints "aMemberVar Member Variable"
 print $foo->{'aMemberVar'}; // Prints "aMemberVar Member Variable"
 ?>

You can use members of other objects as well:

<?php
 print $foo->{$otherObj->var};
print $foo->{$otherObj->func()};
 ?>

You can use mathods above to access member functions as well:

<?php
 print $foo->{'aMemberFunc'}(); // Prints "Inside `aMemberFunc()`"
 print $foo->{$foo->aFuncName}(); // Prints "Inside `aMemberFunc()`"
 ?>
 

 
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