PHPのお勉強！ – Atelier ”慶”

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オーバーロード

PHP におけるオーバーロード機能は、プロパティやメソッドを動的に作成するための手法です。これらの動的エンティティは、マジックメソッドを用いて処理されます。マジックメソッドは、クラス内でさまざまなアクションに対して用意することができます。

オーバーロードメソッドが起動するのは、宣言されていないプロパティやメソッドを操作しようとしたときです。また、現在のスコープからはアクセス不能なプロパティやメソッドを操作しようとしたときにも起動します。このセクションでは、これらの (宣言されていない、あるいは現在のスコープからはアクセス不能な) プロパティやメソッドのことをアクセス不能プロパティおよびアクセス不能メソッドと表記することにします。

オーバーロードメソッドは、すべて public で定義しなければなりません。

注意:
これらのマジックメソッドの引数は、リファレンス渡しとすることはできません。

注意:
PHP におけるオーバーロードの解釈は、他の多くのオブジェクト指向言語とは異なります。一般的に「オーバーロード」とは、「名前は同じだけれども引数の数や型が異なるメソッドを複数用意できる」という機能のことを指します。

プロパティのオーバーロード

public __set(string $name, mixed $value): void

public __get(string $name): mixed

public __isset(string $name): bool

public __unset(string $name): void

__set() は、アクセス不能(protected または private)または存在しないプロパティへデータを書き込む際に実行されます。

__get() は、アクセス不能(protected または private)または存在しないプロパティからデータを読み込む際に使用します。

__isset() は、 isset() あるいは empty() をアクセス不能(protected または private)または存在しないプロパティに対して実行したときに起動します。

__unset() は、 unset() をアクセス不能(protected または private)または存在しないプロパティに対して実行したときに起動します。

引数 $name は、操作しようとしたプロパティの名前です。 __set() メソッドの引数 $value は、 $name に設定しようとした値となります。

プロパティのオーバーロードはオブジェクトのコンテキストでのみ動作します。これらのマジックメソッドは、static メソッドとしては呼び出されません。したがって、これらのメソッドを static メソッドとして宣言してはいけません。マジックメソッドを static メソッドとして宣言すると警告が発生します。

注意:
__set() の戻り値は無視されます。これは、PHP が代入演算子を処理する方法によるものです。同様に __get() は、
 $a = $obj->b = 8; 
のように代入と連結した場合には決してコールされません。

注意:
PHP は、オーバーロードメソッドを、同じオーバーロードメソッドから決してコールしません。これはたとえば、__get() の内部に return $this->foo というコードを書いたとしても、 foo というプロパティが定義されていなければ E_WARNING が発生し、null を返すということです。 2回目の __get() のコールを行ったりはしません。しかし、オーバーロードメソッドが、他のオーバーロードメソッドを暗黙のうちに呼び出す可能性はあります(たとえば、 __set() が __get() を呼び出す場合)。

例1 __get()、 __set()、__isset() および __unset() メソッドを使ったプロパティのオーバーロードの例

<?php
class PropertyTest
{
    /**  オーバーロードされるデータの場所  */
    private $data = array();

    /**  宣言されているプロパティにはオーバーロードは起動しません */
    public $declared = 1;

    /**  クラスの外部からアクセスした場合にのみこれがオーバーロードされます  */
    private $hidden = 2;

    public function __set($name, $value)
    {
        echo "Setting '$name' to '$value'\n";
        $this->data[$name] = $value;
    }

    public function __get($name)
    {
        echo "Getting '$name'\n";
        if (array_key_exists($name, $this->data)) {
            return $this->data[$name];
        }

        $trace = debug_backtrace();
        trigger_error(
            'Undefined property via __get(): ' . $name .
            ' in ' . $trace[0]['file'] .
            ' on line ' . $trace[0]['line'],
            E_USER_NOTICE);
        return null;
    }

    public function __isset($name)
    {
        echo "Is '$name' set?\n";
        return isset($this->data[$name]);
    }

    public function __unset($name)
    {
        echo "Unsetting '$name'\n";
        unset($this->data[$name]);
    }

    /**  マジックメソッドではありません。単なる例として示しています  */
    public function getHidden()
    {
        return $this->hidden;
    }
}


echo "<pre>\n";

$obj = new PropertyTest;

$obj->a = 1;
echo $obj->a . "\n\n";

var_dump(isset($obj->a));
unset($obj->a);
var_dump(isset($obj->a));
echo "\n";

echo $obj->declared . "\n\n";

echo "Let's experiment with the private property named 'hidden':\n";
echo "Privates are visible inside the class, so __get() not used...\n";
echo $obj->getHidden() . "\n";
echo "Privates not visible outside of class, so __get() is used...\n";
echo $obj->hidden . "\n";
?>

上の例の出力は以下となります。

Setting 'a' to '1'
Getting 'a'
1

Is 'a' set?
bool(true)
Unsetting 'a'
Is 'a' set?
bool(false)

1

Let's experiment with the private property named 'hidden':
Privates are visible inside the class, so __get() not used...
2
Privates not visible outside of class, so __get() is used...
Getting 'hidden'


Notice:  Undefined property via __get(): hidden in <file> on line 70 in <file> on line 29

メソッドのオーバーロード

public __call(string $name, array $arguments): mixed

public static __callStatic(string $name, array $arguments): mixed

__call() は、アクセス不能メソッドをオブジェクトのコンテキストで実行したときに起動します。

__callStatic() は、アクセス不能メソッドをstatic メソッドとして呼び出した場合に起動します。

引数 $name は、コールしようとしたメソッドの名前です。引数 $arguments は配列で、メソッド $name に渡そうとしたパラメータが格納されます。

例2 __call() および __callStatic() メソッドによる、メソッドのオーバーロードの例

<?php
class MethodTest
{
    public function __call($name, $arguments)
    {
        // 注意: $name は大文字小文字を区別します
        echo "Calling object method '$name' "
             . implode(', ', $arguments). "\n";
    }

    public static function __callStatic($name, $arguments)
    {
        // 注意: $name は大文字小文字を区別します
        echo "Calling static method '$name' "
             . implode(', ', $arguments). "\n";
    }
}

$obj = new MethodTest;
$obj->runTest('in object context');

MethodTest::runTest('in static context');
?>

上の例の出力は以下となります。

Calling object method 'runTest' in object context
Calling static method 'runTest' in static context

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User Contributed Notes 27 notes

down

376

theaceofthespade at gmail dot com ¶

12 years ago

A word of warning!  It may seem obvious, but remember, when deciding whether to use __get, __set, and __call as a way to access the data in your class (as opposed to hard-coding getters and setters), keep in mind that this will prevent any sort of autocomplete, highlighting, or documentation that your ide mite do.

Furthermore, it beyond personal preference when working with other people.  Even without an ide, it can be much easier to go through and look at hardcoded member and method definitions in code, than having to sift through code and piece together the method/member names that are assembled in __get and __set.

If you still decide to use __get and __set for everything in your class, be sure to include detailed comments and documenting, so that the people you are working with (or the people who inherit the code from you at a later date) don't have to waste time interpreting your code just to be able to use it.

down

272

Anonymous ¶

8 years ago

First off all, if you read this, please upvote the first comment on this list that states that “overloading” is a bad term for this behaviour. Because it REALLY is a bad name. You’re giving new definition to an already accepted IT-branch terminology.

Second, I concur with all criticism you will read about this functionality. Just as naming it “overloading”, the functionality is also very bad practice. Please don’t use this in a production environment. To be honest, avoid to use it at all. Especially if you are a beginner at PHP. It can make your code react very unexpectedly. In which case you MIGHT be learning invalid coding!

And last, because of __get, __set and __call the following code executes. Which is abnormal behaviour. And can cause a lot of problems/bugs.

<?php

class BadPractice {
  // Two real properties
  public $DontAllowVariableNameWithTypos = true;
  protected $Number = 0;
  // One private method
  private function veryPrivateMethod() { }
  // And three very magic methods that will make everything look inconsistent
  // with all you have ever learned about PHP.
  public function __get($n) {}
  public function __set($n, $v) {}
  public function __call($n, $v) {}
}

// Let's see our BadPractice in a production environment!
$UnexpectedBehaviour = new BadPractice;

// No syntax highlighting on most IDE's
$UnexpectedBehaviour->SynTaxHighlighting = false;

// No autocompletion on most IDE's
$UnexpectedBehaviour->AutoCompletion = false;

// Which will lead to problems waiting to happen
$UnexpectedBehaviour->DontAllowVariableNameWithTyphos = false; // see if below

// Get, Set and Call anything you want!
$UnexpectedBehaviour->EveryPosibleMethodCallAllowed(true, 'Why Not?');

// And sure, why not use the most illegal property names you can think off
$UnexpectedBehaviour->{'100%Illegal+Names'} = 'allowed';

// This Very confusing syntax seems to allow access to $Number but because of
// the lowered visibility it goes to __set()
$UnexpectedBehaviour->Number = 10;

// We can SEEM to increment it too! (that's really dynamic! :-) NULL++ LMAO
$UnexpectedBehaviour->Number++;

// this ofcourse outputs NULL (through __get) and not the PERHAPS expected 11
var_dump($UnexpectedBehaviour->Number);

// and sure, private method calls LOOK valid now!
// (this goes to __call, so no fatal error)
$UnexpectedBehaviour->veryPrivateMethod();

// Because the previous was __set to false, next expression is true
// if we didn't had __set, the previous assignment would have failed
// then you would have corrected the typho and this code will not have
// been executed. (This can really be a BIG PAIN)
if ($UnexpectedBehaviour->DontAllowVariableNameWithTypos) {
  // if this code block would have deleted a file, or do a deletion on
  // a database, you could really be VERY SAD for a long time!
  $UnexpectedBehaviour->executeStuffYouDontWantHere(true);
}
?>

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187

egingell at sisna dot com ¶

17 years ago

Small vocabulary note: This is *not* "overloading", this is "overriding".

Overloading: Declaring a function multiple times with a different set of parameters like this:
<?php

function foo($a) {
    return $a;
}

function foo($a, $b) {
    return $a + $b;
}

echo foo(5); // Prints "5"
echo foo(5, 2); // Prints "7"

?>

Overriding: Replacing the parent class's method(s) with a new method by redeclaring it like this:
<?php

class foo {
    function new($args) {
        // Do something.
    }
}

class bar extends foo {
    function new($args) {
        // Do something different.
    }
}

?>

down

Anonymous ¶

9 years ago

Using magic methods, especially __get(), __set(), and __call() will effectively disable autocomplete in most IDEs (eg.: IntelliSense) for the affected classes.

To overcome this inconvenience, use phpDoc to let the IDE know about these magic methods and properties: @method, @property, @property-read, @property-write.

/**
 * @property-read name
 * @property-read price
 */
class MyClass
{
    private $properties = array('name' => 'IceFruit', 'price' => 2.49)
    
    public function __get($name)
    {
        return $this->properties($name);
    }
}

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pogregoire##live.fr ¶

8 years ago

It is important to understand that encapsulation can be very easily violated in PHP. for example :
class Object{

}

$Object = new Object();
$Objet->barbarianProperties  = 'boom';

var_dump($Objet);// object(Objet)#1 (1) { ["barbarianProperties"]=> string(7) "boom" }

Hence it is possible to add a propertie out form the class definition.
It is then a necessity in order to protect encapsulation to introduce __set() in the class :

class Objet{
    public function __set($name,$value){
        throw new Exception ('no');
    }
}

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turabgarip at gmail dot com ¶

3 years ago

I concur that "overloading" is a wrong term for this functionality. But I disagree that this functionality is completely wrong. You can do "bad practice" with right code too.

For example __call() is very well applicable to external integration implementations which I am using to relay calls to SOAP methods which doesn't need local implementation. So you don't have to write "empty body" functions. Consider the SOAP service you connect has a "stock update" method. All you have to do is passing product code and stock count to SOAP.

<?php

class Inventory {

  public __construct() {
    // configure and connect to SOAP service
    $this->soap = new SoapClient();
  }

  public __call($soapMethod, $params) {
    $this->soap->{$soapMethod}(params);
  }
}

 // Now you can use any SOAP method without needing a wrapper
 $stock = new Inventory();
 $stock->updatePrice($product_id, 20);
 $stock->saveProduct($product_info);
 
?>

Of course you'd need a parameter mapping but it's in my honest opinion a lot better then having a plenty of mirror methods like:

<?php

class Inventory {

  public function updateStock($product_id, $stock) {
    $soapClient->updateStock($product_id, $stock;
  }
  public function updatePrice($product_id, $price) {
    $soapClient->updateStock($product_id, $price;
  }
  // ...
}

?>

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Ant P. ¶

16 years ago

Be extra careful when using __call():  if you typo a function call somewhere it won't trigger an undefined function error, but get passed to __call() instead, possibly causing all sorts of bizarre side effects.
In versions before 5.3 without __callStatic, static calls to nonexistent functions also fall through to __call!
This caused me hours of confusion, hopefully this comment will save someone else from the same.

down

gabe at fijiwebdesign dot com ¶

10 years ago

Note that you can enable "overloading" on a class instance at runtime for an existing property by unset()ing that property. 

eg: 

<?php
class Test { 

    public $property1;

    public function __get($name) 
    {
        return "Get called for " . get_class($this) . "->\$$name \n";
    }

}
?>

The public property $property1 can be unset() so that it can be dynamically handled via __get(). 

<?php 
$Test = new Test();
unset($Test->property1); // enable overloading
echo $Test->property1; // Get called for Test->$property1
?>

Useful if you want to proxy or lazy load properties yet want to have documentation and visibility in the code and debugging compared to __get(), __isset(), __set() on non-existent inaccessible properties.

down

johannes dot kingma at gmail dot com ¶

3 years ago

One interesting use of the __get function is property / function colaescence, using the same name for a property and a function. 

Example:
<?php
class prop_fun {
    private $prop = 123;

    public function __get( $property ) {
        if( property_exists( $this, $property ) ){
            return $this-> $property;
        }
        throw new Exception( "no such property $property." );
    }
    public function prop() {
        return 456;
    }
}

$o = new prop_fun();

echo $o-> prop . '<br>' . PHP_EOL;
echo $o-> prop() . '<br>' . PHP_EOL;
?>

This will output 123 and 456. This does look like a funy cludge but I used it of a class containing a date type property and function allowing me to write

<?php
class date_class {
    /** @property int $date */
    private $the_date;

    public function __get( $property ) {
        if( property_exists( $this, $property ) ){
            return $this-> $property;
        }
        throw new Exception( "no such property $property." );
    }
    public function the_date( $datetime ) {
        return strtotime( $datetime, $this-> the_date );
    }

    public function __construct()    {
        $this-> the_date = time();
    }
}

$date_object = new date_class();

$today = $date_object-> the_date;
$nextyear = $date_object-> the_date("+1 year");

echo date( "d/m/Y", $today) . '<br>';
echo date( "d/m/Y", $nextyear );
?>

Which I like because its self documenting properties. I used this in a utility class for user input.

down

navarr at gtaero dot net ¶

14 years ago

If you want to make it work more naturally for arrays $obj->variable[] etc you'll need to return __get by reference.



<?php

class Variables

{

        public function __construct()

        {

                if(session_id() === "")

                {

                        session_start();

                }

        }

        public function __set($name,$value)

        {

                $_SESSION["Variables"][$name] = $value;

        }

        public function &__get($name)

        {

                return $_SESSION["Variables"][$name];

        }

        public function __isset($name)

        {

                return isset($_SESSION["Variables"][$name]);

        }

}

?>

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php at lanar dot com dot au ¶

14 years ago

Note that __isset is not called on chained checks. 
If isset( $x->a->b ) is executed where $x is a class with __isset() declared, __isset() is not called.

<?php

class demo
{
    var $id ;
    function __construct( $id = 'who knows' )
    {
        $this->id = $id ;
    }
    function __get( $prop )
    {
        echo "\n", __FILE__, ':', __LINE__, ' ', __METHOD__, '(', $prop, ') instance ', $this->id ;
        return new demo( 'autocreated' ) ; // return a class anyway for the demo
    }
    function __isset( $prop )
    {
        echo "\n", __FILE__, ':', __LINE__, ' ', __METHOD__, '(', $prop, ') instance ', $this->id ;
        return FALSE ;
    }
}
$x = new demo( 'demo' ) ;
echo "\n", 'Calls __isset() on demo as expected when executing isset( $x->a )' ;
$ret = isset( $x->a ) ;
echo "\n", 'Calls __get() on demo without call to __isset()  when executing isset( $x->a->b )' ;
$ret = isset( $x->a->b ) ;
?>

Outputs

Calls __isset() on demo as expected when executing isset( $x->a )
C:\htdocs\test.php:31 demo::__isset(a) instance demo
Calls __get() on demo without call to __isset()  when executing isset( $x->a->b )
C:\htdocs\test.php:26 demo::__get(a) instance demo
C:\htdocs\test.php:31 demo::__isset(b) instance autocreated

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PHP at jyopp dotKomm ¶

19 years ago

Here's a useful class for logging function calls.  It stores a sequence of calls and arguments which can then be applied to objects later.  This can be used to script common sequences of operations, or to make "pluggable" operation sequences in header files that can be replayed on objects later.

If it is instantiated with an object to shadow, it behaves as a mediator and executes the calls on this object as they come in, passing back the values from the execution.

This is a very general implementation; it should be changed if error codes or exceptions need to be handled during the Replay process.
<?php
class MethodCallLog {
    private $callLog = array();
    private $object;
    
    public function __construct($object = null) {
        $this->object = $object;
    }
    public function __call($m, $a) {
        $this->callLog[] = array($m, $a);
        if ($this->object) return call_user_func_array(array(&$this->object,$m),$a);
        return true;
    }
    public function Replay(&$object) {
        foreach ($this->callLog as $c) {
            call_user_func_array(array(&$object,$c[0]), $c[1]);
        }
    }
    public function GetEntries() {
        $rVal = array();
        foreach ($this->callLog as $c) {
            $rVal[] = "$c[0](".implode(', ', $c[1]).");";
        }
        return $rVal;
    }
    public function Clear() {
        $this->callLog = array();
    }
}

$log = new MethodCallLog();
$log->Method1();
$log->Method2("Value");
$log->Method1($a, $b, $c);
// Execute these method calls on a set of objects...
foreach ($array as $o) $log->Replay($o);
?>

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cottton at i-stats dot net ¶

10 years ago