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gabe at fijiwebdesign dot com
21-May-2007 09:25


In response to sirbinam.

You cannot call a function or method before it exists. In your example, the global instance of stdout is just being passed around to differnet references (pointers). It however exists in the "dump" function scope via the global keyword. 



The code below works fine and illustrates that "stdout" has been defined before its instantiation. 



<?php



class profiler{

  function profiler(){

    $this->starttime = microtime();

  }



  function dump(){

    global $stdout;

    $this->endtime = microtime();

    $duration = $this->endtime - $this->starttime;

    $stdout->write($duration);

  }

}



class stdout{

  function write($msg){

    echo $msg;

  }

}



$stdout =& new stdout();

$profiler =& new profiler();

$profiler->dump();



?>



All classes and functions declarations within a scope exist even before the php execution reaches them. It does not matter if you have your classes defined on the first or last line, as long as they are in the same scope as where they are called and are not in a conditional statement that has not been evaluated yet.

ludvig dot ericson at gmail dot com
18-Aug-2006 03:35


In reply to the usort thing, you can access a property of an object dynamically by:

<?php

$obj = (object)array("Test" => "bar")

$var = "Test";

echo $obj->$var;

?>

This will output "bar", and do notice I call on ->$var and not just ->var.

Trevor Blackbird > yurab.com
26-Nov-2005 09:33


You can create a new object using the built-in stdClass or by using type-casting:



<?php



// This is the proper way

$object1 = new stdClass();



// This works too

$object2 = (object) NULL;



// This will create an object from an array

$monkey_array = array('title'=>'Spider Monkey', 'src'=>'monkey.jpg');

$monkey_object = (object) $monkey_array;

print $monkey_object->title . ' ' . $monkey_object->src;



// You can type-cast in the middle of an expression

function customHTML($some_object) {

// this function expects an object as the argument and returns some output

}

print '<p>Writing some output ' . customHTML( (object) array('rows'=>3, 'cols'=>4) );



?>

james dot jones at firstinvestors dot com
10-Mar-2005 09:32


iblun:



Highly recommended that you NOT try to write your own sort function. Try something like this instead:



<?php



function sort_by_field($obj_array, $field)

{

   return usort($obj_array,

         create_function('$o1,$o2',

              "return (\$o1->$field < \$o2->$field) ? -1 : 1"));

}



?>



(Warning: untested code...)

iblun at gmx dot net
09-Mar-2005 05:08


To sort an array, that contains an object, after one fieldname inside the object, im using this function:



function objectSort($objectarray, $field)

{

    for ($a=0;$a < (count($objectarray)); $a++)

    {

        for ($b=0;$b < (count($objectarray)); $b++)

        {    

            if ($objectarray[$a]->$field < $objectarray[$b]->$field)

            {

                $temp = $objectarray[$a];

                $objectarray[$a] = $objectarray[$b];

                $objectarray[$b] = $temp;

            }

        }

    }

    

    return $objectarray;

}

mortoray at ecircle-ag dot com
16-Feb-2005 02:07


If you use new to create items in an array, you may not get the results you want since the parameters to array will be copies of the original and not references.



By Example:

class Store {

    var $item = 3;

}



    $a = array( new Store() );

    $b = $a;

    $a[0]->item = 2;

    print( "|" . $b[0]->item . "| <br>" );   //shows 3



    $a = array();

    $a[] =& new Store();

    $b = $a;

    $a[0]->item = 2;

    print( "|" . $b[0]->item . "| <br>" );   //shows 2



This is extremely important if you intend on passing arrays of classes to functions and expect them to always use the same object instance!



Note: The following syntax is desired (or maybe even the default notation should translate as this):

   $a = array( &new Store() );

sirbinam at nospam dot please dot hotmail dot com
15-Nov-2004 06:46


<?php



class hack{}

$hack =& new hack;



class profiler{

  function profiler(){

    $this->startime = microtime();

  }



  function dump(){

    global $hack;

    $this->endtime = microtime();

    $duration = $this->endtime - $this->starttime; /* this won't actually work, it just the concept */

    $stdout->write($duration);

  }

}



class stdout{

  function write($msg){

    echo $msg;

  }

}



$stdout =& new stdout();

$hack =& $stdout;

$profiler->dump();



?>



/*

     *

     * In short this little hack allows us to call $stdout->write() from

     * $profiler->dump

     *

     * The problem is that $stdout doesn't exist yet and when the compiler

     * parses this class, it sends a fatal error and dies because you can't

     * refer to a method of an object that doesn't exist yet, even though

     * this method doesn't get called until the end of execution, when the

     * method does exist.

     * This is the same as not being able to use a function before it is

     * at least declared in say a header file. This is seen in C, Perl,

     * and pretty much every language known to man. (TTBOMK?)

     *

     * So what does this hack do?

     * The first thing that happens in the global scope is an empty class

     * definition, it then creates a object called $hack from this class.

     * All this does is allocate memory for an object, and places a pointer

     * at the begining of that memory segment.

     * When the compiler parses this class, it doesn't care that the $hack

     * object is empty, as long as it has somewhere to assign a function

     * pointer. Later in global scope the $stdout object is created.

     * After $stdout is created, we do $hack =& $stdout. The =&

     * (assign by reference) moves the pointer for $hack to the begining of

     * the memory segment for $stdout. So when we call $hack->write(), it

     * points to the exact same object->method() as $stdout->write(). So

     * this is actually very reliable, just don't tell a purist!

     */

jbinam at nospam dot please dot hotmail dot com
15-Nov-2004 06:46


<?php



class hack{}

$hack =& new hack;



class profiler{

  function profiler(){

    $this->startime = microtime();

  }



  function dump(){

    global $hack;

    $this->endtime = microtime();

    $duration = $this->endtime - $this->starttime; /* this won't actually work, it just the concept */

    $stdout->write($duration);

  }

}



class stdout{

  function write($msg){

    echo $msg;

  }

}



$stdout =& new stdout();

$hack =& $stdout;

$profiler->dump();



?>



/*

     *

     * In short this little hack allows us to call $stdout->write() from

     * $profiler->dump

     *

     * The problem is that $stdout doesn't exist yet and when the compiler

     * parses this class, it sends a fatal error and dies because you can't

     * refer to a method of an object that doesn't exist yet, even though

     * this method doesn't get called until the end of execution, when the

     * method does exist.

     * This is the same as not being able to use a function before it is

     * at least declared in say a header file. This is seen in C, Perl,

     * and pretty much every language known to man. (TTBOMK?)

     *

     * So what does this hack do?

     * The first thing that happens in the global scope is an empty class

     * definition, it then creates a object called $hack from this class.

     * All this does is allocate memory for an object, and places a pointer

     * at the begining of that memory segment.

     * When the compiler parses this class, it doesn't care that the $hack

     * object is empty, as long as it has somewhere to assign a function

     * pointer. Later in global scope the $stdout object is created.

     * After $stdout is created, we do $hack =& $stdout. The =&

     * (assign by reference) moves the pointer for $hack to the begining of

     * the memory segment for $stdout. So when we call $hack->write(), it

     * points to the exact same object->method() as $stdout->write(). So

     * this is actually very reliable, just don't tell a purist!

     */

nconantj
18-Jul-2004 12:43


php at electricsurfer.com,



More than a year later and here's some clarification of what's happening in your code, via comments in an otherwise verbatim copy.



<?

class c

{

   var $a = array('a'=>'aa','b'=>'ab');

   var $b = 'c';

  

   function show()

   {

       echo $this->a['a']; // -> 1st

       echo $this->a['b']; // outputs 'ab'

      

       $a = 'a';

       $b = 'b';

      

       echo $this->$a[$a]; // [] 1st, not what I expected

       //Above first becomes $this->$a['a'] by looking at the function's local $a

       //Next it becomes $this->a by again looking at the function's local $a, which references the class variable $a with no subscripts.

       // In order to reference elements of the class variable $a, 

       // you want to use $this->a[$a]



       echo $this->$a[$b]; // does NOT output 'ab'

       // Same as above, but the first step $b becomes 'b'



       $this_a =& $this->$a; // work-around

      

       echo $this_a[$a]; // no question

       echo $this_a[$b];

      

       $a_arr = array('a'=>'b');

      

       echo $this->$a_arr[$a]; // [] 1st => outputs 'c'

       // This becomes $this->$a_arr['a'] which becomes $this->c,

       // by referencing the local variables first.

   }

}

$c = new c();

$c->show();

?>

info at keltoi-web dot com
25-Aug-2003 02:26


PHP supports recursive type definitions as far as I've tried. The class below (a _very_ simple tree) is an example:



class Tree {



var $_value = null;

var $_children = array();



function Tree ($value) {

  $this->_value = $value;

}



function addChild ($value) {

  $aux_node = new Tree ($value);

  $this->_children [] = $aux_node;

  return $aux_node; 

}

}



As you can see, in addChild we reference Tree again...



However, you must be careful about references. See the chapter "References explained" for more details.



Hope this helps.

php at electricsurfer dot com
22-May-2003 09:25


Here's an example on operator precedence between ->  and []

& what happens with $object->$member[$array_element]



<?

class c

{

    var $a = array('a'=>'aa','b'=>'ab');

    var $b = 'c';

    

    function show()

    {

        echo $this->a['a']; // -> 1st

        echo $this->a['b']; // outputs 'ab'

        

        $a = 'a';

        $b = 'b';

        

        echo $this->$a[$a]; // [] 1st, not what I expected

        echo $this->$a[$b]; // does NOT output 'ab'

        

        $this_a =& $this->$a; // work-around

        

        echo $this_a[$a]; // no question

        echo $this_a[$b];

        

        $a_arr = array('a'=>'b');

        

        echo $this->$a_arr[$a]; // [] 1st => outputs 'c'

    }

}

$c = new c();

$c->show();

?>

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