PHP 7.0.6 Released

    The Basics

    class

    Basic class definitions begin with the keyword class, followed by a class name, followed by a pair of curly braces which enclose the definitions of the properties and methods belonging to the class.

    The class name can be any valid label, provided it is not a PHP reserved word. A valid class name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: ^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$.

    A class may contain its own constants, variables (called "properties"), and functions (called "methods").

    Example #1 Simple Class definition

    <?php
    class SimpleClass
    {
            // property declaration
            public $var = 'a default value';

            // method declaration
            public function displayVar() {
            echo     $this->var;
        }
    }
    ?>

    The pseudo-variable $this is available when a method is called from within an object context. $this is a reference to the calling object (usually the object to which the method belongs, but possibly another object, if the method is called statically from the context of a secondary object).

    Example #2 Some examples of the $this pseudo-variable

    <?php
    class A
    {
        function     foo()
        {
            if (isset(    $this)) {
                echo     '$this is defined (';
                echo     get_class($this);
                echo     ")\n";
            } else {
                echo     "\$this is not defined.\n";
            }
        }
    }

    class     B
    {
        function     bar()
        {
                // Note: the next line will issue a warning if E_STRICT is enabled.
                A::foo();
        }
    }

    $a = new A();
    $a->foo();

    // Note: the next line will issue a warning if E_STRICT is enabled.
    A::foo();
    $b = new B();
    $b->bar();

    // Note: the next line will issue a warning if E_STRICT is enabled.
    B::bar();
    ?>

    The above example will output:

    $this is defined (A)
$this is not defined.
$this is defined (B)
$this is not defined.

    new

    To create an instance of a class, the new keyword must be used. An object will always be created unless the object has a constructor defined that throws an exception on error. Classes should be defined before instantiation (and in some cases this is a requirement).

    If a string containing the name of a class is used with new, a new instance of that class will be created. If the class is in a namespace, its fully qualified name must be used when doing this.

    Example #3 Creating an instance

    <?php
    $instance     = new SimpleClass();

    // This can also be done with a variable:
    $className = 'SimpleClass';
    $instance = new $className(); // new SimpleClass()
    ?>

    In the class context, it is possible to create a new object by new self and new parent.

    When assigning an already created instance of a class to a new variable, the new variable will access the same instance as the object that was assigned. This behaviour is the same when passing instances to a function. A copy of an already created object can be made by cloning it.

    Example #4 Object Assignment

    <?php

    $instance     = new SimpleClass();

    $assigned   =  $instance;
    $reference  =& $instance;

    $instance->var = '$assigned will have this value';

    $instance = null; // $instance and $reference become null

    var_dump($instance);
    var_dump($reference);
    var_dump($assigned);
    ?>

    The above example will output:

    NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

    PHP 5.3.0 introduced a couple of new ways to create instances of an object:

    Example #5 Creating new objects

    <?php
    class Test
    {
        static public function     getNew()
        {
            return new static;
        }
    }

    class     Child extends Test
    {}

    $obj1 = new Test();
    $obj2 = new $obj1;
    var_dump($obj1 !== $obj2);

    $obj3 = Test::getNew();
    var_dump($obj3 instanceof Test);

    $obj4 = Child::getNew();
    var_dump($obj4 instanceof Child);
    ?>

    The above example will output:

    bool(true)
bool(true)
bool(true)

    Properties and methods

    Class properties and methods live in separate "namespaces", so it is possible to have a property and a method with the same name. Reffering to both a property and a method has the same notation, and whether a property will be accessed or a method will be called, solely depends on the context, i.e. whether the usage is a variable access or a function call.

    Example #6 Property access vs. method call

    class Foo
    {
        public $bar = 'property';
        
        public function bar() {
            return 'method';
        }
    }

    $obj = new Foo();
    echo $obj->bar, PHP_EOL, $obj->bar(), PHP_EOL;

    The above example will output:

    property
method

    That means that calling an anonymous function which has been assigned to a property is not directly possible. Instead the property has to be assigned to a variable first, for instance.

    Example #7 Calling an anonymous function stored in a property

    class Foo
    {
        public $bar;
        
        public function __construct() {
            $this->bar = function() {
                return 42;
            };
        }
    }

    $obj = new Foo();
    $func = $obj->bar;
    echo $func(), PHP_EOL;

    The above example will output:

    42

    extends

    A class can inherit the methods and properties of another class by using the keyword extends in the class declaration. It is not possible to extend multiple classes; a class can only inherit from one base class.

    The inherited methods and properties can be overridden by redeclaring them with the same name defined in the parent class. However, if the parent class has defined a method as final, that method may not be overridden. It is possible to access the overridden methods or static properties by referencing them with parent::.

    When overriding methods, the parameter signature should remain the same or PHP will generate an E_STRICT level error. This does not apply to the constructor, which allows overriding with different parameters.

    Example #8 Simple Class Inheritance

    <?php
    class ExtendClass extends SimpleClass
    {
            // Redefine the parent method
            function displayVar()
        {
            echo     "Extending class\n";
                parent::displayVar();
        }
    }

    $extended = new ExtendClass();
    $extended->displayVar();
    ?>

    The above example will output:

    Extending class
a default value

    ::class

    Since PHP 5.5, the class keyword is also used for class name resolution. You can get a string containing the fully qualified name of the ClassName class by using ClassName::class. This is particularly useful with namespaced classes.

    Example #9 Class name resolution

    <?php
    namespace NS {
        class     ClassName {
        }
        
        echo     ClassName::class;
    }
    ?>

    The above example will output:

    NS\ClassName

    Note:

    The class name resolution using ::class is a compile time transformation. That means at the time the class name string is created no autoloading has happened yet. As a consequence, class names are expanded even if the class does not exist. No error is issued in that case.

    User Contributed Notes

    aaron at thatone dot com
    8 years ago
    I was confused at first about object assignment, because it's not quite the same as normal assignment or assignment by reference. But I think I've figured out what's going on.

    First, think of variables in PHP as data slots. Each one is a name that points to a data slot that can hold a value that is one of the basic data types: a number, a string, a boolean, etc. When you create a reference, you are making a second name that points at the same data slot. When you assign one variable to another, you are copying the contents of one data slot to another data slot.

    Now, the trick is that object instances are not like the basic data types. They cannot be held in the data slots directly. Instead, an object's "handle" goes in the data slot. This is an identifier that points at one particular instance of an obect. So, the object handle, although not directly visible to the programmer, is one of the basic datatypes.

    What makes this tricky is that when you take a variable which holds an object handle, and you assign it to another variable, that other variable gets a copy of the same object handle. This means that both variables can change the state of the same object instance. But they are not references, so if one of the variables is assigned a new value, it does not affect the other variable.

    <?php
    // Assignment of an object
    Class Object{
       public     $foo="bar";
    };

    $objectVar = new Object();
    $reference =& $objectVar;
    $assignment = $objectVar

    //
    // $objectVar --->+---------+
    //                |(handle1)----+
    // $reference --->+---------+   |
    //                              |
    //                +---------+   |
    // $assignment -->|(handle1)----+
    //                +---------+   |
    //                              |
    //                              v
    //                  Object(1):foo="bar"
    //
    ?>

    $assignment has a different data slot from $objectVar, but its data slot holds a handle to the same object. This makes it behave in some ways like a reference. If you use the variable $objectVar to change the state of the Object instance, those changes also show up under $assignment, because it is pointing at that same Object instance.

    <?php
    $objectVar    ->foo = "qux";
    print_r( $objectVar );
    print_r( $reference );
    print_r( $assignment );

    //
    // $objectVar --->+---------+
    //                |(handle1)----+
    // $reference --->+---------+   |
    //                              |
    //                +---------+   |
    // $assignment -->|(handle1)----+
    //                +---------+   |
    //                              |
    //                              v
    //                  Object(1):foo="qux"
    //
    ?>

    But it is not exactly the same as a reference. If you null out $objectVar, you replace the handle in its data slot with NULL. This means that $reference, which points at the same data slot, will also be NULL. But $assignment, which is a different data slot, will still hold its copy of the handle to the Object instance, so it will not be NULL.

    <?php
    $objectVar     = null;
    print_r($objectVar);
    print_r($reference);
    print_r($assignment);

    //
    // $objectVar --->+---------+
    //                |  NULL   |
    // $reference --->+---------+
    //                          
    //                +---------+
    // $assignment -->|(handle1)----+
    //                +---------+   |
    //                              |
    //                              v
    //                  Object(1):foo="qux"
    ?>
    Doug
    5 years ago
    What is the difference between  $this  and  self ?

    Inside a class definition, $this refers to the current object, while  self  refers to the current class.

    It is necessary to refer to a class element using  self ,
    and refer to an object element using  $this .
    Note also how an object variable must be preceded by a keyword in its definition.

    The following example illustrates a few cases:

    <?php
    class Classy {

    const           STAT = 'S' ; // no dollar sign for constants (they are always static)
    static     $stat = 'Static' ;
    public         $publ = 'Public' ;
    private        $priv = 'Private' ;
    protected      $prot = 'Protected' ;

    function     __construct( ){  }

    public function     showMe( ){
        print     '<br> self::STAT: '  .  self::STAT ; // refer to a (static) constant like this
            print '<br> self::$stat: ' . self::$stat ; // static variable
            print '<br>$this->stat: '  . $this->stat ; // legal, but not what you might think: empty result
            print '<br>$this->publ: '  . $this->publ ; // refer to an object variable like this
            print '<br>' ;
    }
    }
    $me = new Classy( ) ;
    $me->showMe( ) ;

    /* Produces this output:
    self::STAT: S
    self::$stat: Static
    $this->stat:
    $this->publ: Public
    */
    ?>
    Notes on stdClass
    6 years ago
    stdClass is the default PHP object. stdClass has no properties, methods or parent. It does not support magic methods, and implements no interfaces.

    When you cast a scalar or array as Object, you get an instance of stdClass. You can use stdClass whenever you need a generic object instance.
    <?php
    // ways of creating stdClass instances
    $x = new stdClass;
    $y = (object) null;        // same as above
    $z = (object) 'a';         // creates property 'scalar' = 'a'
    $a = (object) array('property1' => 1, 'property2' => 'b');
    ?>

    stdClass is NOT a base class! PHP classes do not automatically inherit from any class. All classes are standalone, unless they explicitly extend another class. PHP differs from many object-oriented languages in this respect.
    <?php
    // CTest does not derive from stdClass
    class CTest {
        public     $property1;
    }
    $t = new CTest;
    var_dump($t instanceof stdClass);            // false
    var_dump(is_subclass_of($t, 'stdClass'));    // false
    echo get_class($t) . "\n";                   // 'CTest'
    echo get_parent_class($t) . "\n";            // false (no parent)
    ?>

    You cannot define a class named 'stdClass' in your code. That name is already used by the system. You can define a class named 'Object'.

    You could define a class that extends stdClass, but you would get no benefit, as stdClass does nothing.

    (tested on PHP 5.2.8)
    wbcarts at juno dot com
    7 years ago
    CLASSES and OBJECTS that represent the "Ideal World"

    Wouldn't it be great to get the lawn mowed by saying $son->mowLawn()? Assuming the function mowLawn() is defined, and you have a son that doesn't throw errors, the lawn will be mowed.

    In the following example; let objects of type Line3D measure their own length in 3-dimensional space. Why should I or PHP have to provide another method from outside this class to calculate length, when the class itself holds all the neccessary data and has the education to make the calculation for itself?

    <?php

    /*
    * Point3D.php
    *
    * Represents one locaton or position in 3-dimensional space
    * using an (x, y, z) coordinate system.
    */
    class Point3D
    {
        public     $x;
        public     $y;
        public     $z;                  // the x coordinate of this Point.

        /*
         * use the x and y variables inherited from Point.php.
         */
            public function __construct($xCoord=0, $yCoord=0, $zCoord=0)
        {
                $this->x = $xCoord;
            $this->y = $yCoord;
                $this->z = $zCoord;
        }

            /*
         * the (String) representation of this Point as "Point3D(x, y, z)".
         */
            public function __toString()
        {
            return     'Point3D(x=' . $this->x . ', y=' . $this->y . ', z=' . $this->z . ')';
        }
    }

    /*
    * Line3D.php
    *
    * Represents one Line in 3-dimensional space using two Point3D objects.
    */
    class Line3D
    {
            $start;
            $end;

        public function     __construct($xCoord1=0, $yCoord1=0, $zCoord1=0, $xCoord2=1, $yCoord2=1, $zCoord2=1)
        {
                $this->start = new Point3D($xCoord1, $yCoord1, $zCoord1);
                $this->end = new Point3D($xCoord2, $yCoord2, $zCoord2);
        }

            /*
         * calculate the length of this Line in 3-dimensional space.
         */
            public function getLength()
        {
            return     sqrt(
                    pow($this->start->x - $this->end->x, 2) +
                    pow($this->start->y - $this->end->y, 2) +
                    pow($this->start->z - $this->end->z, 2)
            );
        }

            /*
         * The (String) representation of this Line as "Line3D[start, end, length]".
         */
            public function __toString()
        {
            return     'Line3D[start=' . $this->start .
                    ', end=' . $this->end .
                    ', length=' . $this->getLength() . ']';
        }
    }

    /*
    * create and display objects of type Line3D.
    */
    echo '<p>' . (new Line3D()) . "</p>\n";
    echo     '<p>' . (new Line3D(0, 0, 0, 100, 100, 0)) . "</p>\n";
    echo     '<p>' . (new Line3D(0, 0, 0, 100, 100, 100)) . "</p>\n";

    ?>

      <--  The results look like this  -->

    Line3D[start=Point3D(x=0, y=0, z=0), end=Point3D(x=1, y=1, z=1), length=1.73205080757]

    Line3D[start=Point3D(x=0, y=0, z=0), end=Point3D(x=100, y=100, z=0), length=141.421356237]

    Line3D[start=Point3D(x=0, y=0, z=0), end=Point3D(x=100, y=100, z=100), length=173.205080757]

    My absolute favorite thing about OOP is that "good" objects keep themselves in check. I mean really, it's the exact same thing in reality... like, if you hire a plumber to fix your kitchen sink, wouldn't you expect him to figure out the best plan of attack? Wouldn't he dislike the fact that you want to control the whole job? Wouldn't you expect him to not give you additional problems? And for god's sake, it is too much to ask that he cleans up before he leaves?

    I say, design your classes well, so they can do their jobs uninterrupted... who like bad news? And, if your classes and objects are well defined, educated, and have all the necessary data to work on (like the examples above do), you won't have to micro-manage the whole program from outside of the class. In other words... create an object, and LET IT RIP!
    Manish Gupta
    4 years ago
    Some thing that may be obvious to the seasoned PHP programmer, but may surprise someone coming over from C++:

    <?php
    class Foo
    {
    $bar = 'Hi There';

    public function Print(){
        echo     $bar;
    }
    }
    ?>

    Gives an error saying Print used undefined variable. One has to explicitly use (notice the use of <?php $this->bar ?>):

    <?php
    class Foo
    {
    $bar = 'Hi There';

    public function Print(){
        echo     this->$bar;
    }
    }
    ?>

    <?php echo $this->bar; ?> refers to the class member, while using $bar means using an uninitialized variable in the local context of the member function.
    Marcus
    5 years ago
    Here's another simple example.

    <?php
    // PHP 5

    // class definition
    class Bear {
            // define properties
            public $name;
        public     $weight;
        public     $age;
        public     $sex;
        public     $colour;

            // constructor
            public function __construct() {
                $this->age = 0;
                $this->weight = 100;
        }

            // define methods
            public function eat($units) {
            echo     $this->name." is eating ".$units." units of food... ";
                $this->weight += $units;
        }

        public function     run() {
            echo     $this->name." is running... ";
        }

        public function     kill() {
            echo     $this->name." is killing prey... ";
        }

        public function     sleep() {
            echo     $this->name." is sleeping... ";
        }
    }

    // extended class definition
    class PolarBear extends Bear {

            // constructor
            public function __construct() {
                parent::__construct();
                $this->colour = "white";
                $this->weight = 600;
        }

            // define methods
            public function swim() {
            echo     $this->name." is swimming... ";
        }
    }

    ?>
    Jeffrey
    7 years ago
    A PHP Class can be used for several things, but at the most basic level, you'll use classes to "organize and deal with like-minded data". Here's what I mean by "organizing like-minded data". First, start with unorganized data.

    <?php
    $customer_name    ;
    $item_name;
    $item_price;
    $customer_address;
    $item_qty;
    $item_total;
    ?>

    Now to organize the data into PHP classes:

    <?php
    class Customer {
          $name;          // same as $customer_name
          $address;       // same as $customer_address
    }

    class     Item {
          $name;          // same as $item_name
          $price;         // same as $item_price
          $qty;           // same as $item_qty
          $total;         // same as $item_total
    }
    ?>

    Now here's what I mean by "dealing" with the data. Note: The data is already organized, so that in itself makes writing new functions extremely easy.

    <?php
    class Customer {
      public     $name, $address;                   // the data for this class...

      // function to deal with user-input / validation
      // function to build string for output
      // function to write -> database
      // function to  read <- database
      // etc, etc
    }

    class     Item {
      public     $name, $price, $qty, $total;        // the data for this class...

      // function to calculate total
      // function to format numbers
      // function to deal with user-input / validation
      // function to build string for output
      // function to write -> database
      // function to  read <- database
      // etc, etc
    }
    ?>

    Imagination that each function you write only calls the bits of data in that class. Some functions may access all the data, while other functions may only access one piece of data. If each function revolves around the data inside, then you have created a good class.
    igor dot pellegrini at diespam-berlinonline dot de
    1 year ago
    It should be noted that the new keyword "::class", added in 5.5, WILL NOT PERFORM ANY CHECK on the existence of the targeted class, either in the current namespace or another.

    If the targeted class has not an explicitly defined namespace the keyword will JUST PROVIDE a fully qualified name corresponding to:

    CURRENT_NAMESPACE + TARGET_CLASS_NAME

    This could NOT correspond to any existing class!

    In PHP >5.x it is possible to 'USE' a non-existing namespace and/or a non-existing class, as long as the class is not really used in the code.
    The interpreter will NOT raise any error in these case:

    - the USEd namespace doesn't exist
    <?php
    use This\Is\Just\A\Fake\Namespace\SomewhereExistantClass as NotFoundClass;
    ?>
    - the class doesn't exist in the defined namespace
    <?php
    use In\This\Valid\Namespace\Doesnt\Exist\The\GhostClass as NonExistentClass;
    ?>
    - the class doesn't exist in the current namespace (when not specifying the class with the 'USE' keyword)
    <?php
    use This\Is\A\Valid\Namespace\GhostClass as NonExistentClass;
    ?>

    So doing something like:
    <?php
    namespace MyProject;

    use     MyProject\WrongNamespace\NonExistingClassName;

    class     Test
    {
        public static function     getNonExistantClass()
        {
            return     NonExistingClassName::class;
        }
    }

    echo     Test::getNonExistantClass();
    ?>
    will print
    "MyProject\WrongNamespace\NonExistingClassName"

    WITHOUT raising any error!

    ----

    So, to recap:
    To avoid tricky side effects, IF you want to USE THE '::CLASS' keyword, ALWAYS REMEMBER TO carefully CHECK IT HAS BEEN DECLARED CORRECTLY in the 'USE' statement (that actually exists in the current or in the defined namespace)
    info at youwanttoremovethisvakantiebaas dot nl
    8 years ago
    if you do this
    <?php

    $x     = new b();

    class     b extends a {}

    class     a { }

    ?>
    PHP will tell you "class b not found", because you've defined class b before a. However, the error tells you something different.... Got me a little confused :)
    moty66 at gmail dot com
    6 years ago
    I hope that this will help to understand how to work with static variables inside a class

    <?php

    class a {

        public static     $foo = 'I am foo';
        public     $bar = 'I am bar';
       
        public static function     getFoo() { echo self::$foo;    }
        public static function     setFoo() { self::$foo = 'I am a new foo'; }
        public function     getBar() { echo $this->bar;    }           
    }

    $ob = new a();
    a::getFoo();     // output: I am foo   
    $ob->getFoo();    // output: I am foo
    //a::getBar();     // fatal error: using $this not in object context
    $ob->getBar();    // output: I am bar
                    // If you keep $bar non static this will work
                    // but if bar was static, then var_dump($this->bar) will output null

    // unset($ob);
    a::setFoo();    // The same effect as if you called $ob->setFoo(); because $foo is static
    $ob = new a();     // This will have no effects on $foo
    $ob->getFoo();    // output: I am a new foo

    ?>

    Regards
    Motaz Abuthiab
    the_french_cow at hotmail dot com
    6 years ago
    For those of us who are new to inheritance, private functions are not visible in an inherited class. Consider:

    <?php
            class A {
            protected function     func1() {
                echo(    "I'm func1 in A!<br/>");
            }

            private function     func2() {
                echo(    "I'm func2 in A!<br/>");
            }
        }
       
        class     B extends A {
            public function     func3() {
                echo(    "I'm func3 in B!<br/>");
                    $this->func1();
                    $this->func2();  // Call to private function from extended class results in a fatal error
                }
        }
       
            $b = new B;
            $b->func3();  // Ends in a fatal error

    // OR

            $b->func1();  // Call to protected function from outside world results in a fatal error
    ?>

    If you want a function to be accessible in class B but not to the outside world, it must be declared as protected.
    php at kingsquare dot nl
    2 years ago
    Just to be clear: the correct way of validating a classname, as stated in the docs is:

    $valid = preg_match('/^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$/', $className);

    (thanks to salathe@php.net & aharvey@php.net for clearing me up!)
    chris (@) xeneco (dot) co (dot) uk
    7 years ago
    Regarding object inheritance:

    I hope this helps someone, it should help if you're new to OOPS

    <?php

    class A {
       
        public     $x = 'A';

        public function     foo() {
                $b = new B;
                $b->bar();
            return     $this->x;
        }
    }

    class     B extends A {
        public function     bar() {
                $this->x = 'B';
        }
    }

    $a = new A

    echo $a->foo();    //A

    ?>

    I was doing something similar to this (example is greatly simplified to show logic) and spent a long while trying to work out why I would always get 'A' and never get 'B'. Now, after a few weeks, I have revisited the problem and have worked out why:

    The code 'new B' creates a new instance of class B. While class B extends class A, it is a new object and not an extension of the object created by 'new A'

    The value of $x is set to 'B' within the object $b, but not in object $a.

    If within A::foo(), one was to access $b->x then one would obtain the vale 'B', for example

    <?php

    class C {
       
        public     $x = 'C';

        public function     foo() {
                $c = new C;
                $c->bar();
                $this->x = $c->$x
                return $this->x;
        }
    }

    class     D extends C {
        public function     bar() {
                $this->x = 'D';
        }
    }

    $c = new C

    echo $c->foo();    //D

    ?>
    ohcc at 163 dot com
    5 months ago
    You can get an empty object by instantiating the StdClass.

    <?php
        $cfg     = new StdClass;
            $cfg->domain = 'www.51-n.com';
        echo     $cfg->domain;
    ?>

    or by json_decode() ...

    <?php
        $cfg     = json_decode('{}');
            $cfg->domain = 'www.51-n.com';
        echo     $cfg->domain;
    ?>
    alan at alan-ng dot net
    8 years ago
    The following odd behavior happens in php version 5.1.4 (and presumably some other versions) that does not happen in php version 5.2.1 (and possibly other versions > 5.1.4).

    <?php

    $_SESSION    ['instance']=...;

    $instance=new SomeClass;

    ?>

    The second line will not only create the $instance object successfully, it will also modify the value of $_SESSION['instance']!

    The workaround I arrived at, after trial and error, was to avoid  using object names which match a $_SESSION array key.

    This is not intended to be a bug report, since it was apparently fixed by version 5.2.1, so it's just a workaround suggestion.
    sklemnov at gmail dot com
    2 years ago
    Small subtlety to anyone just starting out: using $this is for referencing an instance of the current class (there are exceptions to this, but on the basic level it is mostly true; please do not downvote this, it's not meant to be a PhD dissertation).

    For instance,

    class TestClass{
      private $variable = "Hello";
      function ReturnVar(){
        return $this->variable;
      }
      function SetVar($input){
        $this->variable = $input;
      }
    }
    $t = new TestClass();
    echo $t->ReturnVar();
    $t->SetVar("Test");
    echo $t->ReturnVar();

    This is a useless piece of code that illustrates $this in functions.

    echo $t->ReturnVar();

    outputs "Hello", and then:

    $t->SetVar("Test");

    sets the object $t's copy of $variable to "Test". Finally,

    echo $t->ReturnVar();

    returns the new value of $t's copy of $variable, namely "Test".

    using $this in the ReturnVar() function tells PHP that you want to return $t's copy of $variable.

    Suppose we took $this out of the above code:

    class TestClass{
      private $variable = "Hello";
      function ReturnVar(){
        return $variable;
      }
      function SetVar($input){
        $variable= $input;
      }
    }
    $t = new TestClass();
    echo $t->ReturnVar();
    $t->SetVar("Test");
    echo $t->ReturnVar();

    Would show nothing at all! PHP would not know that you meant to reference object $t's version of $variable.
    Dan Dascalescu
    9 years ago
    If E_STRICT is enabled, the first example will generate the following error (and a few others akin to it):

    Non-static method A::foo() should not be called statically on line 26

    The example should have explicitly declared the methods foo() and bar() as static:

    class A                                                                                                                            
    {                                                                                                                                  
        static function foo()                                                                                                          
        {
    ...
    ben dot corne at gmail dot com
    6 years ago
    method calling context aware. By this I mean it will get treated differently while being in a new statement compared to being in a regular call.

    Example:
    <?php
    class Foo {
      private     $className = 'Bar';
     
      public function     make() {
        return new     $this->className();
      }
     
      public function     callClassName() {
           $this->className();
      }

      public function     className() {
        echo     "foo\n";
      }

    };

    class     Bar {
      public function     hello() {
        echo     "bar\n";
      }
    };

    $foo = new Foo();
    $bar = $foo->make();

    echo     "expecting 'bar': ";
    $bar->hello();

    echo     "expecting 'foo': ";
    $foo->callClassName();
    ?>

    even tough $this->className() is written two times in exactly the same way, the one contained in a new statement gets the className field and the other performs the actual method.
    ialsoagree
    7 years ago
    I think it's worth mentioning that if you define a function inside of an object method, that function cannot refer to "$this" - doing so will result in PHP reporting a fatal error:

    Fatal error: Using $this when not in object context

    <?php
    class MyClass {
       public     $message = 'Hello';

       public function     MyClassFunction() {
           function     InnerFunction() {
              echo     $this->message; // Reports a fatal error
               }
               innerFunction();
       }
    }

    $class = new MyClass;
    $class->MyClassFunction();
    ?>

    This issue cannot be solved by using the Scope Resolution Operator if you're trying to access a variable:

    <?php
    class MyClass {
       public     $message = 'Hello';

       public function     MyClassFunction() {
           function     InnerFunction() {
              echo     MyClass::message; // Reports a fatal error
               }
               innerFunction();
       }
    }

    $class = new MyClass;
    $class->MyClassFunction();
    ?>

    Additionally, you can NOT create a public function to access that variable:

    <?php
    class MyClass {
       public     $message = 'Hello';

       public function     MyClassFunction() {
           function     InnerFunction() {
                  MyClass::echoSomething();
           }
               innerFunction();
       }

       public function     echoSomething() {
          echo     $this->message; // Reports a fatal error
           }
    }

    $class = new MyClass;
    $class->MyClassFunction();
    ?>

    Note that in this last case, the error is generated on the line below echoSomething function declaration, not at MyClass::echoSomething();

    However, it is worth noting that when called directly, echoSomething works fine:

    <?php
    class MyClass {
       public     $message = 'Hello';

       public function     MyClassFunction() {
           function     InnerFunction() {
                  MyClass::echoSomething();
           }
               innerFunction();
       }

       public function     echoSomething() {
          echo     $this->message; // Echoes 'Hello'
           }
    }

    $class = new MyClass;
    $class->echoSomething();
    ?>
    ialsoagree
    7 years ago
    Unfortunately, Arpit's solution creates a new class and leaves the old class inaccessible. If you need access to members of the class you are in you'll be unable to get such access. This can be a huge problem.

    However, there is a solution:

    <?php
    class MyClass {
       public     $message = 'Hello';

       public function     MyClassFunction() {
           function     innerFunction(&$this_thing, $message = null) {
                  $this_thing->message = (!is_null($message)) ? $message : $this_thing->message;
                  $this_thing->echo_something();
           }
               innerFunction($this); // echoes 'Hello'
               innerFunction($this, '<br/>New Message'); // echoes '<br/>New Message'
           }
      
       public function     echo_something() {
           echo     $this->message;
       }
    }

    $class = new MyClass;
    $class->MyClassFunction();
    ?>

    By passing $this as a variable by reference, you can access members of the class and even update them. If you don't want to be able to update them, you can simply pass $this to the function but not as a reference.
    alex c
    6 years ago
    ok this really basic but I always forget this. I always get an error like:

    Fatal error: Call to a member function on a non-object

    when i deal with oops

    if it were me finding the error i'd search the internet for hours and then it would occur to me, I'm putting my class operator inside a function, but i would define the class in global file.

    so like this:
    test.php
    <?
    include(class.php);
    $class = new newclassname;

    function function1(){
      $class->dofunc();
    }
    ?>

    you'll get some die errors and try and do this with function1,

    function function1(){
      newclassname::dofunc();
    }

    but if you're using $this inside your class then you'll get another error on non object

    so basically, all you need to do is:

    function function1(){
      $class = new newclassname;
      $class->dofunc();
    }

    or

    function function1(){
      global $class;
      $class->dofunc();
    }

    i know it's simple, but it always gets me!
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