This question already has an answer here:
How to get object like value:item:private from PHP Array
(1 answer)
Closed 7 years ago.
xPostModel Object
(
[script:Model:private] => abc
)
I wanna change abc to efg how can i do it ? Is there any way ?
If you can't make changes to the class definition and there is no public setter method for the class property, and you really need to be able to directly edit the property outside the class, your only option is probably using Reflection methods, see example here: https://stackoverflow.com/a/6448613/1362634
Here is an example that should work in your case to set the private property $script in $obj of type xPostModel (where property is inherited from parent class Model):
$obj = new xPostModel();
$refProperty = new ReflectionProperty('Model', 'script');
$refProperty->setAccessible(true);
$refProperty->setValue($obj, 'def');
And here is a fully working code example with mockup class definitions to simulate the situation of the question.
<?php
error_reporting(-1);
ini_set('display_errors', 1);
class Model {
private $script = 'abc';
}
class xPostModel extends Model {}
$obj = new xPostModel();
print_r($obj); // Check original value of inherited private property
$refProperty = new ReflectionProperty('Model', 'script');
$refProperty->setAccessible(true);
$refProperty->setValue($obj, 'def');
print_r($obj); // Check that property has been changed
Related
I have a object having some protected property that I want to get and set. The object looks like
Fields_Form_Element_Location Object
(
[helper] => formText
[_allowEmpty:protected] => 1
[_autoInsertNotEmptyValidator:protected] => 1
[_belongsTo:protected] =>
[_description:protected] =>
[_disableLoadDefaultDecorators:protected] =>
[_errorMessages:protected] => Array
(
)
[_errors:protected] => Array
(
)
[_isErrorForced:protected] =>
[_label:protected] => Current City
[_value:protected] => 93399
[class] => field_container field_19 option_1 parent_1
)
I want to get value property of the object. When I try $obj->_value or $obj->value it generates error. I searched and found the solution to use PHP Reflection Class. It worked on my local but on server PHP version is 5.2.17 So I cannot use this function there. So any solution how to get such property?
Here's the really simple example (with no error checking) of how to use ReflectionClass:
function accessProtected($obj, $prop) {
$reflection = new ReflectionClass($obj);
$property = $reflection->getProperty($prop);
$property->setAccessible(true);
return $property->getValue($obj);
}
I know you said you were limited to 5.2, but that was 2 years ago, 5.5 is the oldest supported version and I'm hoping to help people with modern versions.
Object can be typecasted into (associative) array and the protected members have keys prefixed with chr(0).'*'.chr(0) (see #fardelian's comment here). Using this undocummented feature you can write an "exposer":
function getProtectedValue($obj, $name) {
$array = (array)$obj;
$prefix = chr(0).'*'.chr(0);
return $array[$prefix.$name];
}
Alternatively, you can parse the value from serialized string, where (it seems) protected members have the same prefix.
This works in PHP 5.2 without the overhead of ReflectionClass. However, there are reasons why some property is protected and hidden from client code. The reading or writing can make the data inconsistent or the author provides some other way to expose it in effort to make the interface as lean as possible. When there are reasons to read the protected property directly, the then-correct approach was to implement __get() magic method, so always check if there is any and see what it does. This counter intuitive lookup was finally solved in PHP 8.1 with readonly properties.
Since PHP 8.0, there also attributes metadata accessible by ReflectionClass, make sure to check them also before performing attempts to break into protected members. Attributes superseded "Annotations"1, so check them, too.
1: annotations are a very nasty surprise to client coders: they parse comments to add crazy fancy black-box useless confusing functionality, should not be used anymore, but they still exist
That's what "protected" is meant for, as the Visibility chapter explains:
Members declared protected can be accessed only within the class itself and by inherited and parent classes.
If you need to access the property from outside, pick one:
Don't declare it as protected, make it public instead
Write a couple of functions to get and set the value (getters and setters)
If you don't want to modify the original class (because it's a third-party library you don't want to mess) create a custom class that extends the original one:
class MyFields_Form_Element_Location extends Fields_Form_Element_Location{
}
... and add your getter/setter there.
If you want to tinker with a class without adding getters and setters....
PHP 7 adds a call($obj) method (faster than old bindTo) on closures allowing you to call a function so the $this variable will act just as it would within a class -with full permissions.
//test class with restricted properties
class test{
protected $bar="protected bar";
private $foo="private foo";
public function printProperties(){
echo $this->bar."::".$this->foo;
}
}
$testInstance=new test();
//we can change or read the restricted properties by doing this...
$change=function(){
$this->bar="I changed bar";
$this->foo="I changed foo";
};
$change->call($testInstance);
$testInstance->printProperties();
//outputs I changed bar::I changed foo in php 7.0
For PHP 7.4+, we can use an Arrow Function and the Closure::call to access private and protected members using just one small line:
PHP 7.4+
Retrieving protected/private members:
class Test {
protected $data = 'Protected variable!';
}
// Will output "Protected variable!"
echo (fn() => $this->data)->call(new Test);
Altering protected/private members:
class Test {
protected $data = 'Testing';
}
$test = new Test;
(fn() => $this->data = "New Data!")->call($test);
// Will output "New Data!"
echo (fn() => $this->data)->call($test);
Of course, we can use a normal Closure function if we want to alter/use multiple members:
class Test {
protected $data = 'Data!';
}
$test = new Test;
(function() {
$this->new_data = "New {$this->data}";
})->call($test);
// Will output "New Data!"
echo (fn() => $this->new_data)->call($test);
If you cannot modify the original class and extending it is not an option either, you can use the ReflectionProperty interface.
The phptoolcase library has a handy method for this:
$value = PtcHandyMan::getProperty($your_object , 'propertyName');
Static property from a singleton class:
$value = PtcHandyMan::getProperty('myCLassName', 'propertyName');
You can find the tool here: http://phptoolcase.com/guides/ptc-hm-guide.html
$a=json_encode((array)$obj);
$b=(array)json_decode(str_replace('\u0000*\u0000','',$a));
echo($b['value']);
What I like to do is declare every property that would be writable from outside as public. The properties that you want to be visible for the outside world but not writable you should declare as protected and write __get() magic method so you can read them. Example:
/**
* Class Test
*
* #property int $protected
*
*/
class Test
{
private const READABLE = ['protected'];
protected $protected = 1;
public $public = 2;
public function __get($property)
{
//if you want to read every protected or private
return $this->$property ?? null;
//if you want only some protected and private values to be readable
if (in_array($property, self::READABLE)) {
return $this->$property;
}
}
}
$test = new Test();
echo $test->protected; //outputs 1
echo $test->public; //outputs 2
$test->protected = 3; //outputs error - protected property
The best would be to have property declaration like:
public readonly $protected = 1; //only readable from the outside
public $public = 2; //readable and writable from the outside
but no such syntax exists yet(or... at least I don't know about it). P.S. you should declare the protected/private properties that will be readable in the Class DockBlock as shown, so you can autocomplete them, otherwise you will be able to access them, but your IDE won't recognize them on autocomplete when you are writing code.
I have a object having some protected property that I want to get and set. The object looks like
Fields_Form_Element_Location Object
(
[helper] => formText
[_allowEmpty:protected] => 1
[_autoInsertNotEmptyValidator:protected] => 1
[_belongsTo:protected] =>
[_description:protected] =>
[_disableLoadDefaultDecorators:protected] =>
[_errorMessages:protected] => Array
(
)
[_errors:protected] => Array
(
)
[_isErrorForced:protected] =>
[_label:protected] => Current City
[_value:protected] => 93399
[class] => field_container field_19 option_1 parent_1
)
I want to get value property of the object. When I try $obj->_value or $obj->value it generates error. I searched and found the solution to use PHP Reflection Class. It worked on my local but on server PHP version is 5.2.17 So I cannot use this function there. So any solution how to get such property?
Here's the really simple example (with no error checking) of how to use ReflectionClass:
function accessProtected($obj, $prop) {
$reflection = new ReflectionClass($obj);
$property = $reflection->getProperty($prop);
$property->setAccessible(true);
return $property->getValue($obj);
}
I know you said you were limited to 5.2, but that was 2 years ago, 5.5 is the oldest supported version and I'm hoping to help people with modern versions.
Object can be typecasted into (associative) array and the protected members have keys prefixed with chr(0).'*'.chr(0) (see #fardelian's comment here). Using this undocummented feature you can write an "exposer":
function getProtectedValue($obj, $name) {
$array = (array)$obj;
$prefix = chr(0).'*'.chr(0);
return $array[$prefix.$name];
}
Alternatively, you can parse the value from serialized string, where (it seems) protected members have the same prefix.
This works in PHP 5.2 without the overhead of ReflectionClass. However, there are reasons why some property is protected and hidden from client code. The reading or writing can make the data inconsistent or the author provides some other way to expose it in effort to make the interface as lean as possible. When there are reasons to read the protected property directly, the then-correct approach was to implement __get() magic method, so always check if there is any and see what it does. This counter intuitive lookup was finally solved in PHP 8.1 with readonly properties.
Since PHP 8.0, there also attributes metadata accessible by ReflectionClass, make sure to check them also before performing attempts to break into protected members. Attributes superseded "Annotations"1, so check them, too.
1: annotations are a very nasty surprise to client coders: they parse comments to add crazy fancy black-box useless confusing functionality, should not be used anymore, but they still exist
That's what "protected" is meant for, as the Visibility chapter explains:
Members declared protected can be accessed only within the class itself and by inherited and parent classes.
If you need to access the property from outside, pick one:
Don't declare it as protected, make it public instead
Write a couple of functions to get and set the value (getters and setters)
If you don't want to modify the original class (because it's a third-party library you don't want to mess) create a custom class that extends the original one:
class MyFields_Form_Element_Location extends Fields_Form_Element_Location{
}
... and add your getter/setter there.
If you want to tinker with a class without adding getters and setters....
PHP 7 adds a call($obj) method (faster than old bindTo) on closures allowing you to call a function so the $this variable will act just as it would within a class -with full permissions.
//test class with restricted properties
class test{
protected $bar="protected bar";
private $foo="private foo";
public function printProperties(){
echo $this->bar."::".$this->foo;
}
}
$testInstance=new test();
//we can change or read the restricted properties by doing this...
$change=function(){
$this->bar="I changed bar";
$this->foo="I changed foo";
};
$change->call($testInstance);
$testInstance->printProperties();
//outputs I changed bar::I changed foo in php 7.0
For PHP 7.4+, we can use an Arrow Function and the Closure::call to access private and protected members using just one small line:
PHP 7.4+
Retrieving protected/private members:
class Test {
protected $data = 'Protected variable!';
}
// Will output "Protected variable!"
echo (fn() => $this->data)->call(new Test);
Altering protected/private members:
class Test {
protected $data = 'Testing';
}
$test = new Test;
(fn() => $this->data = "New Data!")->call($test);
// Will output "New Data!"
echo (fn() => $this->data)->call($test);
Of course, we can use a normal Closure function if we want to alter/use multiple members:
class Test {
protected $data = 'Data!';
}
$test = new Test;
(function() {
$this->new_data = "New {$this->data}";
})->call($test);
// Will output "New Data!"
echo (fn() => $this->new_data)->call($test);
If you cannot modify the original class and extending it is not an option either, you can use the ReflectionProperty interface.
The phptoolcase library has a handy method for this:
$value = PtcHandyMan::getProperty($your_object , 'propertyName');
Static property from a singleton class:
$value = PtcHandyMan::getProperty('myCLassName', 'propertyName');
You can find the tool here: http://phptoolcase.com/guides/ptc-hm-guide.html
$a=json_encode((array)$obj);
$b=(array)json_decode(str_replace('\u0000*\u0000','',$a));
echo($b['value']);
What I like to do is declare every property that would be writable from outside as public. The properties that you want to be visible for the outside world but not writable you should declare as protected and write __get() magic method so you can read them. Example:
/**
* Class Test
*
* #property int $protected
*
*/
class Test
{
private const READABLE = ['protected'];
protected $protected = 1;
public $public = 2;
public function __get($property)
{
//if you want to read every protected or private
return $this->$property ?? null;
//if you want only some protected and private values to be readable
if (in_array($property, self::READABLE)) {
return $this->$property;
}
}
}
$test = new Test();
echo $test->protected; //outputs 1
echo $test->public; //outputs 2
$test->protected = 3; //outputs error - protected property
The best would be to have property declaration like:
public readonly $protected = 1; //only readable from the outside
public $public = 2; //readable and writable from the outside
but no such syntax exists yet(or... at least I don't know about it). P.S. you should declare the protected/private properties that will be readable in the Class DockBlock as shown, so you can autocomplete them, otherwise you will be able to access them, but your IDE won't recognize them on autocomplete when you are writing code.
I have a object having some protected property that I want to get and set. The object looks like
Fields_Form_Element_Location Object
(
[helper] => formText
[_allowEmpty:protected] => 1
[_autoInsertNotEmptyValidator:protected] => 1
[_belongsTo:protected] =>
[_description:protected] =>
[_disableLoadDefaultDecorators:protected] =>
[_errorMessages:protected] => Array
(
)
[_errors:protected] => Array
(
)
[_isErrorForced:protected] =>
[_label:protected] => Current City
[_value:protected] => 93399
[class] => field_container field_19 option_1 parent_1
)
I want to get value property of the object. When I try $obj->_value or $obj->value it generates error. I searched and found the solution to use PHP Reflection Class. It worked on my local but on server PHP version is 5.2.17 So I cannot use this function there. So any solution how to get such property?
Here's the really simple example (with no error checking) of how to use ReflectionClass:
function accessProtected($obj, $prop) {
$reflection = new ReflectionClass($obj);
$property = $reflection->getProperty($prop);
$property->setAccessible(true);
return $property->getValue($obj);
}
I know you said you were limited to 5.2, but that was 2 years ago, 5.5 is the oldest supported version and I'm hoping to help people with modern versions.
Object can be typecasted into (associative) array and the protected members have keys prefixed with chr(0).'*'.chr(0) (see #fardelian's comment here). Using this undocummented feature you can write an "exposer":
function getProtectedValue($obj, $name) {
$array = (array)$obj;
$prefix = chr(0).'*'.chr(0);
return $array[$prefix.$name];
}
Alternatively, you can parse the value from serialized string, where (it seems) protected members have the same prefix.
This works in PHP 5.2 without the overhead of ReflectionClass. However, there are reasons why some property is protected and hidden from client code. The reading or writing can make the data inconsistent or the author provides some other way to expose it in effort to make the interface as lean as possible. When there are reasons to read the protected property directly, the then-correct approach was to implement __get() magic method, so always check if there is any and see what it does. This counter intuitive lookup was finally solved in PHP 8.1 with readonly properties.
Since PHP 8.0, there also attributes metadata accessible by ReflectionClass, make sure to check them also before performing attempts to break into protected members. Attributes superseded "Annotations"1, so check them, too.
1: annotations are a very nasty surprise to client coders: they parse comments to add crazy fancy black-box useless confusing functionality, should not be used anymore, but they still exist
That's what "protected" is meant for, as the Visibility chapter explains:
Members declared protected can be accessed only within the class itself and by inherited and parent classes.
If you need to access the property from outside, pick one:
Don't declare it as protected, make it public instead
Write a couple of functions to get and set the value (getters and setters)
If you don't want to modify the original class (because it's a third-party library you don't want to mess) create a custom class that extends the original one:
class MyFields_Form_Element_Location extends Fields_Form_Element_Location{
}
... and add your getter/setter there.
If you want to tinker with a class without adding getters and setters....
PHP 7 adds a call($obj) method (faster than old bindTo) on closures allowing you to call a function so the $this variable will act just as it would within a class -with full permissions.
//test class with restricted properties
class test{
protected $bar="protected bar";
private $foo="private foo";
public function printProperties(){
echo $this->bar."::".$this->foo;
}
}
$testInstance=new test();
//we can change or read the restricted properties by doing this...
$change=function(){
$this->bar="I changed bar";
$this->foo="I changed foo";
};
$change->call($testInstance);
$testInstance->printProperties();
//outputs I changed bar::I changed foo in php 7.0
For PHP 7.4+, we can use an Arrow Function and the Closure::call to access private and protected members using just one small line:
PHP 7.4+
Retrieving protected/private members:
class Test {
protected $data = 'Protected variable!';
}
// Will output "Protected variable!"
echo (fn() => $this->data)->call(new Test);
Altering protected/private members:
class Test {
protected $data = 'Testing';
}
$test = new Test;
(fn() => $this->data = "New Data!")->call($test);
// Will output "New Data!"
echo (fn() => $this->data)->call($test);
Of course, we can use a normal Closure function if we want to alter/use multiple members:
class Test {
protected $data = 'Data!';
}
$test = new Test;
(function() {
$this->new_data = "New {$this->data}";
})->call($test);
// Will output "New Data!"
echo (fn() => $this->new_data)->call($test);
If you cannot modify the original class and extending it is not an option either, you can use the ReflectionProperty interface.
The phptoolcase library has a handy method for this:
$value = PtcHandyMan::getProperty($your_object , 'propertyName');
Static property from a singleton class:
$value = PtcHandyMan::getProperty('myCLassName', 'propertyName');
You can find the tool here: http://phptoolcase.com/guides/ptc-hm-guide.html
$a=json_encode((array)$obj);
$b=(array)json_decode(str_replace('\u0000*\u0000','',$a));
echo($b['value']);
What I like to do is declare every property that would be writable from outside as public. The properties that you want to be visible for the outside world but not writable you should declare as protected and write __get() magic method so you can read them. Example:
/**
* Class Test
*
* #property int $protected
*
*/
class Test
{
private const READABLE = ['protected'];
protected $protected = 1;
public $public = 2;
public function __get($property)
{
//if you want to read every protected or private
return $this->$property ?? null;
//if you want only some protected and private values to be readable
if (in_array($property, self::READABLE)) {
return $this->$property;
}
}
}
$test = new Test();
echo $test->protected; //outputs 1
echo $test->public; //outputs 2
$test->protected = 3; //outputs error - protected property
The best would be to have property declaration like:
public readonly $protected = 1; //only readable from the outside
public $public = 2; //readable and writable from the outside
but no such syntax exists yet(or... at least I don't know about it). P.S. you should declare the protected/private properties that will be readable in the Class DockBlock as shown, so you can autocomplete them, otherwise you will be able to access them, but your IDE won't recognize them on autocomplete when you are writing code.
I have a object having some protected property that I want to get and set. The object looks like
Fields_Form_Element_Location Object
(
[helper] => formText
[_allowEmpty:protected] => 1
[_autoInsertNotEmptyValidator:protected] => 1
[_belongsTo:protected] =>
[_description:protected] =>
[_disableLoadDefaultDecorators:protected] =>
[_errorMessages:protected] => Array
(
)
[_errors:protected] => Array
(
)
[_isErrorForced:protected] =>
[_label:protected] => Current City
[_value:protected] => 93399
[class] => field_container field_19 option_1 parent_1
)
I want to get value property of the object. When I try $obj->_value or $obj->value it generates error. I searched and found the solution to use PHP Reflection Class. It worked on my local but on server PHP version is 5.2.17 So I cannot use this function there. So any solution how to get such property?
Here's the really simple example (with no error checking) of how to use ReflectionClass:
function accessProtected($obj, $prop) {
$reflection = new ReflectionClass($obj);
$property = $reflection->getProperty($prop);
$property->setAccessible(true);
return $property->getValue($obj);
}
I know you said you were limited to 5.2, but that was 2 years ago, 5.5 is the oldest supported version and I'm hoping to help people with modern versions.
Object can be typecasted into (associative) array and the protected members have keys prefixed with chr(0).'*'.chr(0) (see #fardelian's comment here). Using this undocummented feature you can write an "exposer":
function getProtectedValue($obj, $name) {
$array = (array)$obj;
$prefix = chr(0).'*'.chr(0);
return $array[$prefix.$name];
}
Alternatively, you can parse the value from serialized string, where (it seems) protected members have the same prefix.
This works in PHP 5.2 without the overhead of ReflectionClass. However, there are reasons why some property is protected and hidden from client code. The reading or writing can make the data inconsistent or the author provides some other way to expose it in effort to make the interface as lean as possible. When there are reasons to read the protected property directly, the then-correct approach was to implement __get() magic method, so always check if there is any and see what it does. This counter intuitive lookup was finally solved in PHP 8.1 with readonly properties.
Since PHP 8.0, there also attributes metadata accessible by ReflectionClass, make sure to check them also before performing attempts to break into protected members. Attributes superseded "Annotations"1, so check them, too.
1: annotations are a very nasty surprise to client coders: they parse comments to add crazy fancy black-box useless confusing functionality, should not be used anymore, but they still exist
That's what "protected" is meant for, as the Visibility chapter explains:
Members declared protected can be accessed only within the class itself and by inherited and parent classes.
If you need to access the property from outside, pick one:
Don't declare it as protected, make it public instead
Write a couple of functions to get and set the value (getters and setters)
If you don't want to modify the original class (because it's a third-party library you don't want to mess) create a custom class that extends the original one:
class MyFields_Form_Element_Location extends Fields_Form_Element_Location{
}
... and add your getter/setter there.
If you want to tinker with a class without adding getters and setters....
PHP 7 adds a call($obj) method (faster than old bindTo) on closures allowing you to call a function so the $this variable will act just as it would within a class -with full permissions.
//test class with restricted properties
class test{
protected $bar="protected bar";
private $foo="private foo";
public function printProperties(){
echo $this->bar."::".$this->foo;
}
}
$testInstance=new test();
//we can change or read the restricted properties by doing this...
$change=function(){
$this->bar="I changed bar";
$this->foo="I changed foo";
};
$change->call($testInstance);
$testInstance->printProperties();
//outputs I changed bar::I changed foo in php 7.0
For PHP 7.4+, we can use an Arrow Function and the Closure::call to access private and protected members using just one small line:
PHP 7.4+
Retrieving protected/private members:
class Test {
protected $data = 'Protected variable!';
}
// Will output "Protected variable!"
echo (fn() => $this->data)->call(new Test);
Altering protected/private members:
class Test {
protected $data = 'Testing';
}
$test = new Test;
(fn() => $this->data = "New Data!")->call($test);
// Will output "New Data!"
echo (fn() => $this->data)->call($test);
Of course, we can use a normal Closure function if we want to alter/use multiple members:
class Test {
protected $data = 'Data!';
}
$test = new Test;
(function() {
$this->new_data = "New {$this->data}";
})->call($test);
// Will output "New Data!"
echo (fn() => $this->new_data)->call($test);
If you cannot modify the original class and extending it is not an option either, you can use the ReflectionProperty interface.
The phptoolcase library has a handy method for this:
$value = PtcHandyMan::getProperty($your_object , 'propertyName');
Static property from a singleton class:
$value = PtcHandyMan::getProperty('myCLassName', 'propertyName');
You can find the tool here: http://phptoolcase.com/guides/ptc-hm-guide.html
$a=json_encode((array)$obj);
$b=(array)json_decode(str_replace('\u0000*\u0000','',$a));
echo($b['value']);
What I like to do is declare every property that would be writable from outside as public. The properties that you want to be visible for the outside world but not writable you should declare as protected and write __get() magic method so you can read them. Example:
/**
* Class Test
*
* #property int $protected
*
*/
class Test
{
private const READABLE = ['protected'];
protected $protected = 1;
public $public = 2;
public function __get($property)
{
//if you want to read every protected or private
return $this->$property ?? null;
//if you want only some protected and private values to be readable
if (in_array($property, self::READABLE)) {
return $this->$property;
}
}
}
$test = new Test();
echo $test->protected; //outputs 1
echo $test->public; //outputs 2
$test->protected = 3; //outputs error - protected property
The best would be to have property declaration like:
public readonly $protected = 1; //only readable from the outside
public $public = 2; //readable and writable from the outside
but no such syntax exists yet(or... at least I don't know about it). P.S. you should declare the protected/private properties that will be readable in the Class DockBlock as shown, so you can autocomplete them, otherwise you will be able to access them, but your IDE won't recognize them on autocomplete when you are writing code.
What I would like to do is have a static factory function that you can give a series of attributes and it returns an object that is of a previously undeclared class that extends a known class.
Basically:
<?php
class foo {
public $a;
function increment($b = 1){
$this->a += $b;
}
}
function factory($name, $a){
//returns an object of class $name that extends foo with $this->a set to $a
}
so that if I write the code:
<?php
$bar = factory("bar",12);
$bar->increment(5);
print_r($bar);
if(is_a($bar, "foo")){
echo "is a Foo";
}
$moo = factory("moo", 4);
$moo->increment();
print_r($moo);
if(is_a($moo, "foo")){
echo "is a Foo";
}
I get: [edit]
bar Object
(
[a] => 17
)
is a Foo
moo Object
(
[a] => 5
)
is a Foo
But I don't know where to start looking for the commands necessary to do this. I think that in my factory function I need to somehow declare that the value of $name extends parent class but makes no changes to it, then constructs a new $name. That way it has all the functionality of the parent class, just a different type.
Check out the PHP reflection API has the methods you need to extract and build the new class there but, how to go about doing it and then creating an instance of it im not sure of. I do know its possible though because im pretty sure this is how Mocking works in PHPUnit. You might also want to look at the various Mock object related classes in PHPUnit to get some ideas as well.
That said unless you are actually adding/overloading methods, why would you even want to do this? Why not just use a property in the object or use a an interface? Whats the goal here?