对象

对象初始化

要初始化一个对象,用 new 语句将对象实例到一个变量中。

<?php
class foo
{
    function
do_foo()
    {
        echo
"Doing foo.";
    }
}

$bar = new foo;
$bar->do_foo();
?>

完整的讨论见类与对象一章。

转换为对象

如果将一个对象转换成对象,它将不会有任何变化。如果其它任何类型的值被转换成对象,内置类 stdClass 的一个实例将被建立。如果该值为 NULL,则新的实例为空。对于任何其它的值,名为 scalar 的成员变量将包含该值。

<?php
$obj
= (object) 'ciao';
echo
$obj->scalar;  // outputs 'ciao'
?>


add a note add a note User Contributed Notes
ludvig dot ericson at gmail dot com
19-Aug-2006 06:35
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
27-Nov-2005 01:33
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
11-Mar-2005 01:32
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 09:08
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 06:07
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
16-Nov-2004 10:46
<?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
16-Nov-2004 10:46
<?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
19-Jul-2004 03:43
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
26-Aug-2003 05:26
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
23-May-2003 12:25
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();
?>