I've found the piece of code below in several places around the web and even here on Stack Overflow, but I just can't wrap my head around it. I know what it does, but I don't know how it does it even with the examples. Basically it's storing values, but I don't know how I add values to the registry. Can someone please try to explain how this code works, both how I set and retrieve values from it?
class Registry {
private $vars = array();
public function __set($key, $val) {
$this->vars[$key] = $val;
}
public function __get($key) {
return $this->vars[$key];
}
}
It's using PHP's hacked on property overloading to add entries to and retrieve entries from the private $vars array.
To add a property, you would use...
$registry = new Registry;
$registry->foo = "foo";
Internally, this would add a foo key to the $vars array with string value "foo" via the magic __set method.
To retrieve a value...
$foo = $registry->foo;
Internally, this would retrieve the foo entry from the $vars array via the magic __get method.
The __get method should really be checking for non-existent entries and handle such things. The code as-is will trigger an E_NOTICE error for an undefined index.
A better version might be
public function __get($key)
{
if (array_key_exists($key, $this->vars)) {
return $this->vars[$key];
}
// key does not exist, either return a default
return null;
// or throw an exception
throw new OutOfBoundsException($key);
}
You might want to check out PHP.NET - Overloading
Basically, you would do...
$Registry = new Registry();
$Registry->a = 'a'; //Woo I'm using __set
echo $Registry->a; //Wooo! I'm using __get
So here, I'm using __set($a, 'This value is not visible to the scope or nonexistent')
Also, I'm using __get($a);
Hope this helped!
Related
Can I assign to a property a value in the constructor, without define any parameter, using for instance an external function?
Example
function my_external_function() {
return 'Good Morning World';
}
class MyClass {
protected $_my_property;
public function __construct() {
$this->_my_property = my_external_function() != '' ? my_external_function() : 'Good night World!';
}
public function getOtherMethod() {
return $this->_my_property;
}
}
$obj = new MyClass();
echo $obj->getOtherMethod();
You can do this. The code in your question will work, but there is a problem with this approach.
If you write your class this way, it will always depend on that external function, but it will have no control over whether or not it even exists, let alone whether or not it will return a value the constructor can use. If you move, rename, or modify the external function, it could change the behavior of your class in unpredictable ways.
I would recommend something like this instead, which I think may accomplish what you're trying to accomplish (not sure) without forcing your class to blindly depend on an external function.
class MyClass {
protected $_my_property = 'Good night World!'; // set a default value here
public function __construct($x = null) { // give your constructor an optional argument
if ($x) { // use the optional argument if it's provided
$this->_my_property = $x;
}
}
public function getOtherMethod() {
return $this->_my_property;
}
}
You can still create an instance of your class with no argument
$obj = new MyClass();
and when you call $obj->getOtherMethod(); you'll get the default value.
You can still use the external function; just let it pass its value into your object's constructor instead of using it within the constructor.
$obj = new MyClass(my_external_function());
Yes, but you better avoid such tricky dependencies.
I have a class with a method that returns a new instance of itself.
This allows me to use one single object without having to declare new ones over and over with the same values. For those wondering why not extending the class or something else, it just makes my life easier and it works like a charm, but my final purpose is to remove them all in one line.
for example:
$foo = new myClass('name1','ab','cd');
$bar = $foo->duplicate();
//duplicate() saves the new object in itself in an array:
array_push($this->instance,new myClass('name1','ab','cd'));
//and returns a pointer to the saved instance.
return end($this->instance);
$foo and $bar now share the same methods and values but those values can be modified separately.
$foo->changeName('newName');
$bar->changeName('newName2');
My question here is, if I unset the first class created unset($foo) will PHP automatically unset the other instances ($bar) or will the garbage collector remove them eventually?
I have tested it by unsettling $foo and gives me an error when I call $foo but not when I call $bar.
What I am trying to do is to unset all the instances of that class at once.
Thanks.
Automatic cleanup?
No, PHP isn't awared about your architecture. It will not remove objects "cascade", they are independent entities - and, more, can belong to different scopes, for example. Simple code:
class Test
{
protected $id = null;
protected $uniqid = null;
public function __construct($id)
{
$this->id = $id;//user-passed variable
$this->uniqid = uniqid();//internal: to identify instance
}
public function getCopy()
{
return new self($this->id);
}
public function getIdentity()
{
return $this->uniqid;
}
}
$foo = new Test(3);
$bar = $foo->getCopy();
var_dump($foo->getIdentity());//valid
unset($foo);
//still valid: bar has nothing to do with foo
var_dump($bar->getIdentity());
By the way, for copying you can use clone in PHP (that, however, will result in object cloning, obviously)
Simple way
Most simple way to resolve a matter is to iterate through $GLOBALS, checking it with instanceof. This has serious weakness: inner function/method scopes would not be affected:
//static since doesn't belong to any instance:
public static function cleanup()
{
foreach($GLOBALS as $name=>$var)
{
if($var instanceof self)
{
unset($GLOBALS[$name]);
}
}
}
-and
$foo = new Test(3);
$bar = $foo->getCopy();
var_dump($foo->getIdentity(), $bar->getIdentity());//valid
Test::cleanup();
//2 x notice:
var_dump($foo, $bar);
Note, that is has nothing to do with "child" mechanics (i.e. it will clean all instances in global scope - no matter which was copied from which).
Common case
Sample above will not do the stuff in common case. Why? Imagine that you'll have holder class:
class Holder
{
protected $obj = null;
public function __construct($obj)
{
$this->obj = $obj;
}
public function getData()
{
return $this->obj;
}
}
and you'll pass instance to it:
$foo = new Test(3);
$bar = $foo->getCopy();
$baz = new Holder($bar);
-so then you'll have no chances to handle even this simple situation in common case. And with more complex situations you will also be stuck.
What to do?
I'd recommend: destroy objects explicitly when you need to do that. Implicit unset is a side-effect, and even if you'll maintain that somehow (I can imagine Observer pattern + some global registry for that) - it will be horrible side-effect, that will kill readability for your code. And same is about code, that uses $GLOBALS I've written above - I do not recommend to act such way in any case.
Try the below code to clear all php objects.
public function clearAllVars()
{
$vars = get_object_vars($this);
foreach($vars as $key => $val)
{
$this->$key = null;
}
}
}
From what I understand from the PHP reference here :
http://www.php.net/manual/en/features.gc.refcounting-basics.php
destroying the main instance will not automatically destroy all other instances since they do not ultimately point to the same 'zval'.
However the garbage collection will eventually destroy all instances if they are not referenced anymore. Since in your example $bar still references the second instance, it will not be destroyed.
What you could do if you want to unset them all at the same time :
Use a static array referencing all the instances of your object
Every time you create a new object add a reference to this object in the static array of the class
Use a static function unsetAll() which loops through this array and unset one by one all instances
I can't quite understand why the output of this code is '1'.
My guess is that php is not behaving like most other OO languages that I'm used to, in that the arrays that php uses must not be objects. Changing the array that is returned by the class does not change the array within the class. How would I get the class to return an array which I can edit (and has the same address as the one within the class)?
<?php
class Test
{
public $arr;
public function __construct()
{
$this->arr = array();
}
public function addToArr($i)
{
$this->arr[] = $i;
}
public function getArr()
{
return $this->arr;
}
}
$t = new Test();
$data = 5;
$t->addToArr($data);
$tobj_arr = $t->getArr();
unset($tobj_arr[0]);
$tobj_arr_fresh = $t->getArr();
echo count($tobj_arr_fresh);
?>
EDIT: I expected the output to be 0
You have to return the array by reference. That way, php returns a reference to the array, in stead of a copy.
<?php
class Test
{
public $arr;
public function __construct()
{
$this->arr = array();
}
public function addToArr($i)
{
$this->arr[] = $i;
}
public function & getArr() //Returning by reference here
{
return $this->arr;
}
}
$t = new Test();
$data = 5;
$t->addToArr($data);
$tobj_arr = &$t->getArr(); //Reference binding here
unset($tobj_arr[0]);
$tobj_arr_fresh = $t->getArr();
echo count($tobj_arr_fresh);
?>
This returns 0.
From the returning references subpage:
Unlike parameter passing, here you have to use & in both places - to
indicate that you want to return by reference, not a copy, and to
indicate that reference binding, rather than usual assignment, should
be done
Note that although this gets the job done, question is if it is a good practice. By changing class members outside of the class itself, it can become very difficult to track the application.
Because array are passed by "copy on write" by default, getArr() should return by reference:
public function &getArr()
{
return $this->arr;
}
[snip]
$tobj_arr = &$t->getArr();
For arrays that are object, use ArrayObject. Extending ArrayObject is probably better in your case.
When you unset($tobj_arr[0]); you are passing the return value of the function call, and not the actual property of the object.
When you call the function again, you get a fresh copy of the object's property which has yet to be modified since you added 5 to it.
Since the property itself is public, try changing:
unset($tobj_arr[0]);
To: unset($t->arr[0]);
And see if that gives you the result you are looking for.
You are getting "1" because you are asking PHP how many elements are in the array by using count. Remove count and use print_r($tobj_arr_fresh)
First, a quote from the ole' manual on ArrayAccess::offsetSet():
This function is not called in assignments by reference and otherwise indirect changes to array dimensions overloaded with ArrayAccess (indirect in the sense they are made not by changing the dimension directly, but by changing a sub-dimension or sub-property or assigning the array dimension by reference to another variable). Instead, ArrayAccess::offsetGet() is called. The operation will only be successful if that method returns by reference, which is only possible since PHP 5.3.4.
I'm a bit confused by this. It appears that this suggests that (as of 5.3.4) one can define offsetGet() to return by reference in an implementing class, thus handling assignments by reference.
So, now a test snippet:
(Disregard the absence of validation and isset() checking)
class Test implements ArrayAccess
{
protected $data = array();
public function &offsetGet($key)
{
return $this->data[$key];
}
public function offsetSet($key, $value)
{
$this->data[$key] = $value;
}
public function offsetExists($key) { /* ... */ }
public function offsetUnset($key) { /* ... */ }
}
$test = new Test();
$test['foo'] = 'bar';
$test['foo'] = &$bar; // Fatal error: Cannot assign by reference to
// overloaded object in
var_dump($test, $bar);
Ok, so that doesn't work. Then what does this manual note refer to?
Reason
I'd like to permit assignment by reference via the array operator to an object implementing ArrayAccess, as the example snippet shows. I've investigated this before, and I didn't think it was possible, but having come back to this due to uncertainty, I (re-)discovered this mention in the manual. Now I'm just confused.
Update: As I hit Post Your Question, I realized that this is likely just referring to assignment by reference to another variable, such as $bar = &$test['foo'];. If that's the case, then apologies; though knowing how, if it is at all possible, to assign by reference to the overloaded object would be great.
Further elaboration: What it all comes down to, is I would like to have the following method aliases:
isset($obj[$key]); // $obj->has_data($key);
$value = $obj[$key]; // $obj->get_data($key);
$obj[$key] = $value; // $obj->set_data($key, $value);
$obj[$key] = &$variable; // $obj->bind_data($key, $variable);
// also, flipping the operands is a syntactic alternative
$variable = &$obj[$key]; // $obj->bind_data($key, $variable);
unset($obj[$key]); // $obj->remove_data($key);
As far as has, get, set, and remove go, they're no problem with the supported methods of ArrayAccess. The binding functionality is where I'm at a loss, and am beginning to accept that the limitations of ArrayAccess and PHP are simply prohibitive of this.
What the manual is referring to are so called "indirect modifications". Consider the following script:
$array = new ArrayObject;
$array['foo'] = array();
$array['foo']['bar'] = 'foobar';
In the above script $array['foo'] = array(); will trigger a offsetSet('foo', array()). $array['foo']['bar'] = 'foobar'; on the other hand will trigger a offsetGet('foo'). Why so? The last line will be evaluated roughly like this under the hood:
$tmp =& $array['foo'];
$tmp['bar'] = 'foobar';
So $array['foo'] is first fetched by ref and then modified. If your offsetGet returns by ref this will succeed. If not you'll get some indirect modification error.
What you want on the other hand is the exact opposite: Not fetch a value by reference, but assign it. This would theoretically require a signature of offsetSet($key, &$value), but practically this is just not possible.
By the way, references are hard to grasp. You'll get lots of non-obvious behavior and this is especially true for array item references (those have some special rules). I'd recommend you to just avoid them altogether.
This does not work with ArrayAccess, you could add yourself a public function that allows you to set a reference to an offset (sure, this looks different to using array syntax, so it's not really a sufficient answer):
class Test implements ArrayAccess{
protected $_data = array();
public function &offsetGet($key){
return $this->_data[$key];
}
...
public function offsetSetReference($key, &$value)
{
$this->_data[$key] = &$value;
}
}
$test = new Test();
$test['foo'] = $var = 'bar';
$test->offsetSetReference('bar', $var);
$var = 'foo';
echo $test['bar']; # foo
$alias = &$test['bar'];
$alias = 'hello :)';
echo $var; # hello :)
Probably such a function was forgotten when ArrayAccess was first implemented.
Edit: Pass it as "a reference assignment":
class ArrayAccessReferenceAssignment
{
private $reference;
public function __construct(&$reference)
{
$this->reference = &$reference;
}
public function &getReference()
{
$reference = &$this->reference;
return $reference;
}
}
class Test implements ArrayAccess{
...
public function offsetSet($key, $value){
if ($value instanceof ArrayAccessReferenceAssignment)
{
$this->offsetSetReference($key, $value->getReference());
}
else
{
$this->_data[$key] = $value;
}
}
Which then works flawlessly because you implemented it. That's probably more nicely interfacing than the more explicit offsetSetReference variant above:
$test = new Test();
$test['foo'] = $var = 'bar';
$test['bar'] = new ArrayAccessReferenceAssignment($var);
$var = 'foo';
echo $test['bar']; # foo
$alias = &$test['bar'];
$alias = 'hello :)';
echo $var; # hello :)
I'm not sure if this is a trivial questions but in a PHP class:
MyClass:
class MyClass {
public $var1;
public $var2;
constructor() { ... }
public method1 () {
// Dynamically create an instance variable
$this->var3 = "test"; // Public....?
}
}
Main:
$test = new MyClass();
$test->method1();
echo $test->var3; // Would return "test"
Does this work?? How would I get this to work? Ps. I wrote this quickly so please disregard any errors I made with setting up the class or calling methods!
EDIT
What about making these instance variables that I create private??
EDIT 2
Thanks all for responding - Everyone is right - I should have just tested it out myself, but I had an exam the next morning and had this thought while studying that I wanted to check to see if it worked. People keep suggesting that its bad OOP - maybe but it does allow for some elegant code. Let me explain it a bit and see if you still think so. Here's what I came up with:
//PHP User Model:
class User {
constructor() { ... }
public static find($uid) {
$db->connect(); // Connect to the database
$sql = "SELECT STATEMENT ...WHERE id=$uid LIMIT 1;";
$result = $db->query($sql); // Returns an associative array
$user = new User();
foreach ($result as $key=>$value)
$user->$$key = $value; //Creates a public variable of the key and sets it to value
$db->disconnect();
}
}
//PHP Controller:
function findUser($id) {
$User = User::find($id);
echo $User->name;
echo $User->phone;
//etc...
}
I could have just put it in an associative array but I can never correctly name that array something meaningful (ie. $user->data['name'] ... ugly.) Either way you have to know what is in the database so I do not really understand what the argument is that its confusing, especially since you can just var dump objects for debugging.
Why dont you just write the code and see for yourself?
<?php
class Foo
{
public function __construct()
{
$this->bar = 'baz';
}
}
$foo = new Foo;
echo $foo->bar; // outputs 'baz'
and
var_dump($foo);
gives
object(Foo)#1 (1) {
["bar"] => string(3) "baz"
}
but
$r = new ReflectionObject($foo);
$p = $r->getProperty('bar');
var_dump($p->isPublic());
will throw an Exception about 'bar' being unknown, while
$r = new ReflectionObject($foo);
$p = $r->getProperties();
var_dump($p[0]->isPublic());
will return true.
Now, should you do this type of assignment? Answer is no. This is not good OOP design. Remember, OOP is about encapsulation. So, if bar is describing some public property of the class, make it explicit and declare it in your class as public $bar. If it is supposed to be private declare it as private $bar. Better yet, dont use public properties at all and make them protected and provide access to them only through getters and setters. That will make the interface much more clearer and cleaner as it conveys what interaction is supposed to be possible with an object instance.
Assigning properties on the fly here and there across your code, will make maintaining your code a nightmare. Just imagine somewhere along the lifecylce of Foo someone does this:
$foo = new Foo;
$foo->monkey = 'ugh';
echo $foo->monkey; // outputs 'ugh'
Now, from looking at the class definition above, there is absolutely no way, a developer can see there is now a monkey patched into Foo. This will make debugging a pain, especially if code like this is frequent and distributed across multiple files.
Yes that will indeed work. Auto-created instance variables are given public visibility.
yes that works as you'd hope/expect.
I you wanted to make private variables on the fly you could use php magic functions to emulate this, e.g
MyClass
<?php
class MyClass {
public $var1;
public $var2;
private $data = array();
public function __get($key) {
// for clarity you could throw an exception if isset($this->data[$key])
// returns false as it is entirely possible for null to be a valid return value
return isset($this->data[$key]) ? return $this->data[$key] : null;
}
public function __set($key, $value) {
$this->data[$key] = $value;
}
}
?>
Main
<?php
$test = new MyClass();
$test->myVar = 'myVar is technically private, i suppose';
echo $this->myVar; // 'myVar is technically private
?>
Although these dynamically created variables are technically private, they are infact publicly accessible... i cannot image the purpose for wanting to dynamically create private instance variables. I would question your design.
Did you try it?
It is possible but you might get strict errors. If you dynamically need to create these variables, you are probably doing something wrong.
You should either change this into a function:
function var($no) { .. }
or use __get (http://ca.php.net/manual/en/language.oop5.overloading.php#language.oop5.overloading.members)