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To create a new object, use the new statement to instantiate a class:
<?php
class foo
{
function do_foo()
{
echo "Doing foo.";
}
}
$bar = new foo;
$bar->do_foo();
?>
For a full discussion, see the Classes and Objects chapter.
If an object is converted to an object, it is not modified. If a value of any other type is converted to an object, a new instance of the stdClass built-in class is created. If the value was NULL, the new instance will be empty. Arrays convert to an object with properties named by keys, and corresponding values. For any other value, a member variable named scalar will contain the value.
<?php
$obj = (object) 'ciao';
echo $obj->scalar; // outputs 'ciao'
?>
i would like to share a curious behavior on casted objects. Casting an object from a class with private/protected attributes results a stdClass with a private/protected attribute for get.
Example:
<?PHP
class Foo{
private $priv = 1;
public $pub = 2;
public function getSimple(){
return (object)(array) $this; //the array cast is to force a stdClass result
}
}
$bar = new Foo();
var_dump($bar->getSimple();// output: object(stdClass)#3 (2) { ["priv:private"]=> int(1) ["pub"]=> int(2) }
var_dump($bar->getSimple()->priv);// output: NULL, not a Fatal Error
var_dump($bar->getSimple()->pub);// output: int(2)
$barSimple = $bar->getSimple();
$barSimple->priv = 10;
var_dump($barSimple->priv);// output: int(10)
?>
Initialization, Instantiation and Instances are terms that can be confusing at first. Let's try to sort it out starting with this simple class definition.
<?php
class User
{
public $first_name;
public $last_name;
public function __toString()
{
return "User [first='$this->first_name', last='$this->last_name']";
}
}
?>
Now create several INSTANCES of User by INSTANTIATING the User class above.
<?php
$user_1 = new User; // $user_1 is an INSTANCE of User
$user_2 = new User; // $user_2 is an INSTANCE of User
echo $user_1 . '<br>'; // User [first='', last='']
echo $user_2 . '<br>'; // User [first='', last='']
?>
Here we have (2) two INSTANCES of User, but each instance was only INSTANTIATED once - when we used the 'new' operator.
And now looking at the printed output, you can see there are no values for their first or last names. This means that the objects themselves have NOT been INITIALIZED. To remedy this situation, rewrite the class definition by adding a __construct() method.
<?php
class User
{
public $first_name;
public $last_name;
public function __construct($first, $last) // Require first and last names when INSTANTIATING
{
$this->first_name = $first; // INITIALIZE $first_name;
$this->last_name = $last; // INITIALIZE $last_name;
}
public function __toString()
{
return "User [first='$this->first_name', last='$this->last_name']";
}
}
?>
Now try it again.
<?php
$user_1 = new User('John', 'Doe'); // $user_i is an INSTANCE of User
$user_2 = new User('Jane', 'Doe'); // $user_2 is an INSTANCE of User
echo $user_1 . '<br>'; // prints: User [first='John', last='Doe']
echo $user_2 . '<br>'; // prints: User [first='Jane', last='Doe']
?>
The __construct() method is called automatically by PHP when it sees the 'new' operator. Our __construct() method above requires the first and last names to be passed in as arguments and uses them to INITIALIZE objects when INSTANTIATING new INSTANCES.
You can create [recursive] objects with something like:
<?php
$literalObjectDeclared = (object) array(
'foo' => (object) array(
'bar' => 'baz',
'pax' => 'vax'
),
'moo' => 'ui'
);
print $literalObjectDeclared->foo->bar; // outputs "baz"!
?>
If having
class BugDetails extends Bug
you want to cast an object of a Bug to BugDetails like this
<?php
$clone = (BugDetails) clone $this;
// OR
$clone = (BugDetails) $bug;
?>
which doesn't work in PHP, you have two options:
1. Copying all (including private) properties manually (you could also use get_object_vars(), but this is shorter):
<?php
$clone = new BugDetails();
foreach ($this as $key => $val) {
$clone->$key = $val;
}
?>
2. Serialize an object Bug, manipulate the resulting string so that it has BugDetails inside and unserialize it.
See here: http://blog.adaniels.nl/articles/a-dark-corner-of-php-class-casting/
Spent two hours looking for more elegant solution, that's my findings.
CAUTION:
"Arrays convert to an object with properties named by keys, and corresponding values".
This is ALWAYS true, which means that even numeric keys are accepted when converting.
But the resulting properties cannot be accessed, since they don't match the variables naming rules.
So this:
<?php
$x = (object) array('a'=>'A', 'b'=>'B', 'C');
echo '<pre>'.print_r($x, true).'</pre>';
?>
works and displays:
stdClass Object
(
[a] => A
[b] => B
[0] => C
)
But this:
<?php
echo '<br />'.$x->a;
echo '<br />'.$x->b;
echo '<br />'.$x->{0}; # (don't use $x->0, which is obviously a syntax error)
?>
fails and displays:
A
B
Notice: Undefined property: stdClass::$0 in...
I saw there was some confusing about what the & operator does in php in relation to objects. So I made an illustrative example:
<?php
class Test {
}
class Test2 {
}
print "---\n";
/* A normal assignment makes test2 into a reference to the object
result:
---
object(Test)#1 (0) {
}
object(Test2)#2 (0) {
}
*/
$test1 = new Test;
$test2 = $test1;
$test2 = new Test2;;
print var_dump($test1);
print var_dump($test2);
/* If we use & we make test2 a reference to $test1
result:
---
object(Test2)#2 (0) {
}
object(Test2)#2 (0) {
}
try instead $test2 = 'pipo';
*/
print "---\n";
$test1 = new Test;
$test2 =& $test1;
$test2 = new Test2;
print var_dump($test1);
print var_dump($test2);
/* If we want to prevent, we ever overwrite what is in $test1, we can do the following:
$test2 =& new Test2;
I don't understand what happens here exactly.
result:
---
object(Test)#3 (0) {
}
object(Test2)#2 (0) {
}
*/
print "---\n";
$test1 = new Test;
$test2 =& $test1;
$test2 =& new Test2;
print var_dump($test1);
print var_dump($test2);
?>
ON-THE-FLY!!!
In response to Bobs note below (and Rick's somewhat): It is much better to predefine the object you want to create. This is because in all the programs you write, you will still create objects On-the-Fly anyway:
$foo = 'My String Object'; // on-the-fly!
$bar = 45; // on-the-fly!
$obj = new stdClass(); // on-the-fly!
$obj->blah = 3; // on-the-fly!
So what's missing above? Real control over WHAT your program does, HOW it does it, and HOW your data is organized. Let's say your code $obj->blah = 3 was 'blah' because 3 was your last Test Score (take no offense, I've done worse!). In that case, you could use code like so:
<?php
class Test{
const MIN = 0, MAX = 100; // acceptable range for a test
protected $person; // person taking the test
protected $score; // use the word 'score' because 'blah' is meaningless
public function __construct($p, $s){
$this->person = $p;
$this->score = self::clamp($s);
}
protected static function clamp($val){
if($val < self::MIN) $val = self::MIN;
if($val > self::MAX) $val = self::MAX;
return $val;
}
public function __toString(){
return "Test [person=$this->person, score=$this->score%]";
}
}
$obj = new Test("John Doe", 83); // on-the-fly!
echo (object)$obj; // outputs 'Test [person=John Doe, score=83%]'
?>
Writing your own class definitions help maintain the "integerity" of your objects - see how the clamp() function keeps test scores between 0 and 100 percent? PHP uses similar techniques to set min and max vals on Numbers. And, classes like Test are way more useful than objects created with an empty shell, uh em, stdClass. In addition, you can see WHAT, WHERE, WHY, and HOW your program actually works... On-the-Fly!
-->
In response to Harmor and Mithras, you can use the json functions to convert multi-dimensional arrays to objects very reliably.
Also, note that just using (object)$x doesn't allow you to access properties inline. For example, this is invalid:
<?php
$x = array("foo"=>"bar");
echo ((object)$x)->foo; // PHP Parse error, unexpected T_OBJECT_OPERATOR
?>
However, this function will let you do that, and will also handle multi-dimensional arrays without any hassle.
<?php
function to_object ($x) {
return (is_object($x) || is_array($x)) ? json_decode(json_encode($x)) : (object) $x;
}
echo to_object( array("foo"=>"bar") )->foo; // "bar"
?>
Note that *numeric* arrays will not be converted to objects using this method.
In response to harmor: if an array contains another array as a value, you can recursively convert all arrays with:
<?php
function arrayToObject( $array ){
foreach( $array as $key => $value ){
if( is_array( $value ) ) $array[ $key ] = arrayToObject( $value );
}
return (object) $array;
}
?>
Bob, I think you solution is to use stdClass and add properties on the fly...
$obj = new stdClass();
$obj->data ="This is the solution";
Why is there nothing in the docs about instantiating a generic object? ie new object() - it does not work.
If one wants to create a dynamic object on the fly, the only option I see is to create it implicitly, by creating a child of it - ghetto:
unset($obj);
$obj->blah = 3;
Environment: PHP/5.2.5
Note that multi-dimentional arrays are not converted to objects, only the first level is like this:
Input:
<?php
$arr = array('nameOfAKey'=>array('subKeyName'=>'itsValue'));
$obj = (object)$arr;
echo '01: '.print_r($obj->nameOfAKey, true).'<br />'; //As expected
echo '02: Test: ('.var_export($obj->nameOfAKey->subKeyName,true).')' //Not supported
?>
Output:
01: Array ( [subKeyName] => itsValue )
02: Test: (NULL)
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.
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.
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) );
?>
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...)
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;
}
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() );
<?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!
*/
<?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!
*/
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();
?>
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.
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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