PHP casting array to object inside a class. Is that possible?

Question

I have a variable like

$a = array(
       'first' => array( 'b' => 2, 'c' => 3),
       'second' => array('d' => 4, 'e' => 5)
);

To access an element, I can use

$a['first']['c']

But to access it like this,

$a->first->c

I can cast the array into object as follows:

$a = (object)array(
       'first' => (object)array( 'b' => 2, 'c' => 3),
       'second' => (object)array('d' => 4, 'e' => 5)
);

But i have to use the same inside a class like this..

class className {
     public static $a = (object)array(
           'first' => (object)array( 'b' => 2, 'c' => 3),
           'second' => (object)array('d' => 4, 'e' => 5)
    );
}

It throws a T_OBJECT_CAST error. How can i make it work, if i want to access the element like

className::$a->first->c;

Answer 1

Note that static member variable shares the memory among all objects of same class

You can try this:

LIVE DEMO

<?php

class sample
{

     public static $a;

     function __construct() {

          self::$a = (object)array(
                   'first' => (object)array( 'b' => 2, 'c' => 3),
                   'second' => (object)array('d' => 4, 'e' => 5)
                    );
     }

}

// $obj = new sample();
var_dump(sample::$a->first);

Answer 2

Currently, you can not use expressions in default class properties definitions. Only plain values can be used for that. In future PHP versions it will be allowed to use static expressions ( this RFC is by Bob Weinand ) in such definitions (ie expressions which can be evaluated instantly, not in run-time).

You'll have to use constructor to define your property value, like:

public function __construct()
{
   //non-static property:
   $this->a = (object)array(
           'first' => (object)array( 'b' => 2, 'c' => 3),
           'second' => (object)array('d' => 4, 'e' => 5)
    );
}

-for normal properties. For static properties, of course, you can use self:: - but it will not be bound to instantiation (obviously, that's because it's static)

By the way, there's a trick with array to object conversion:

$a = array(
       'first' => array( 'b' => 2, 'c' => 3),
       'second' => array('d' => 4, 'e' => 5)
);

//object:
$a = json_decode(json_encode($a));

Answer 3

Constant expressions in PHP are rather limited right now (though there are some changes in the works). You can initialize the static variable after the class definition, or in a static initialization function, which you will need to call explicitly.

class ClassName {
     public static $a;
}
ClassName::$a = (object)array(
       'first' => (object)array( 'b' => 2, 'c' => 3),
       'second' => (object)array('d' => 4, 'e' => 5),
    );

The advantage of using an initialization function is that you can encapsulate other class initialization tasks. If there aren't other tasks, it can be overkill.

class ClassName {
    public static $a;
    static function initialize() {
        static $notRun = TRUE;
        if ($notRun) {
            $notRun = FALSE;
            self::$a = (object)array(
              'first' => (object)array( 'b' => 2, 'c' => 3),
              'second' => (object)array('d' => 4, 'e' => 5),
            );
            # other tasks...
        }
    }
}
ClassName::initialize();

Answer 4

class Foo {
    public static $a;

    public function __construct() {
        $a = array(
            'first' => array( 'b' => 2, 'c' => 3 ),
            'second' => array( 'd' => 4, 'e' => 5 )
        );
        self::$a = json_decode( json_encode( $a ) );
    }
}

$foo = new Foo();

var_dump( $foo::$a->first->c );