PHP 7.1.0 Release Candidate 3 Released

O básico

class

A definição de uma classe começa com a palavra chave class, seguida do nome da classe, seguido de um par de colchetes que englobam as definições de propriedades e métodos pertecentes à classe.

O nome de uma classe tem de ser válido, que não seja uma palavra reservada do PHP. Um nome de classe válido começa com uma letra ou sublinhado, seguido de qualquer sequência de letras, números e sublinhados. Como uma expressão regular, pode ser expressada assim: ^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$.

Uma classe pode conter suas próprias constantes, variáveis (chamadas de "propriedades") e funções (chamadas de "métodos").

Exemplo #1 Definição Simples de uma Classe

<?php
class SimpleClass
{
    
// declaração de propriedade
    
public $var 'um valor padrão';

    
// declaração de método
    
public function displayVar() {
        echo 
$this->var;
    }
}
?>

A pseudo-variável $this está disponível quando um método é chamado a partir de um contexto de objeto. $this é uma referência ao objeto chamado (normalmente o objeto ao qual o método pertence, mas possivelmente outro objeto, se o método é chamado estaticamente a partir do contexto de um objeto secundário).

Exemplo #2 Alguns exemplos da pseudo variável $this

<?php
class A
{
    function 
foo()
    {
        if (isset(
$this)) {
            echo 
'$this está definida (';
            echo 
get_class($this);
            echo 
")\n";
        } else {
            echo 
"\$this não está definida.\n";
        }
    }
}

class 
B
{
    function 
bar()
    {
        
// Nota: a próxima linha pode lançar um warning E_STRICT.
        
A::foo();
    }
}

$a = new A();
$a->foo();

// Nota: a próxima linha pode lançar um warning E_STRICT.
A::foo();
$b = new B();
$b->bar();

// Nota: a próxima linha pode lançar um warning E_STRICT.
B::bar();
?>

O exemplo acima irá imprimir:

$this está definida (A)
$this não está definida.
$this está definida (B)
$this não está definida.

new

Para criar uma instância de uma classe, a instrução new deve ser utilizada. Um objeto sempre será criado a não ser que a classe tenha um construtor definido que dispare uma exceção em caso de erro. Classes devem ser definidas antes de instanciadas (e em alguns casos isso é obrigatório).

Se uma string contendo o nome da classe é utilizado com new, uma nova instância da classe será criada. Se a classe estiver dentro de um namespace, o nome completo e qualificado deve ser utilizado para fazer isso.

Exemplo #3 Criando uma instância

<?php
$instance 
= new SimpleClass();

// Também pode ser feito com uma variável:
$className 'SimpleClass';
$instance = new $className(); // new SimpleClass()
?>

No contexto da classe, é possível criar um novo objeto com new self e new parent.

Ao atribuir uma instância de uma classe já criada, a uma variável nova, a variável nova irá acessar a mesma instância do objeto que foi atribuído. Este comportamento se mantém ao se passar instâncias a uma função. Uma cópia de um objeto criado pode ser feita clonando o mesmo.

Exemplo #4 Atribuição de Objetos

<?php

$instance 
= new SimpleClass();

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

$instance->var '$assigned terá esse valor';

$instance null// $instance e $reference tornam-se nulos

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

O exemplo acima irá imprimir:

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned terá esse valor"
}

O PHP 5.3.0 introduziu algumas novas formas de criar instâncias de um objeto:

Exemplo #5 Criando novos objetos

<?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);
?>

O exemplo acima irá imprimir:

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

Propriedades e métodos

Propriedades e métodos de classe vivem em "namespaces" separados, de forma que é possível ter uma propriedade e método com mesmos nomes. A referência a propriedades e métodos tem a mesma notação, e a decisão de se uma propriedade será acessada ou uma chamada a um método feita, depende somente do contexto, ou seja, se está tentando acessar uma variável ou chamar um método.

Exemplo #6 Acesso a propriedade vs. chamar um método

class Foo
{
    public $bar = 'propriedade';

    public function bar() {
        return 'métod';
    }
}

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

O exemplo acima irá imprimir:

propriedade
método

Isto significa que chamar diretamente uma função anônima atribuída a uma propriedade não é possível. Em vez disso, por exemplo, a propriedade deve primeiro ser atribuída a uma variável. A partir do PHP 7.0.0, é possível chamar uma propriedade diretamente a colocando entre parênteses.

Exemplo #7 Chamando uma função anônima armazenada em uma propriedade

class Foo
{
    public $bar;

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

$obj = new Foo();

// a partir do PHP 5.3.0:
$func = $obj->bar;
echo $func(), PHP_EOL;

// alternativamente, a partir do PHP 7.0.0:
echo ($obj->bar)(), PHP_EOL;

O exemplo acima irá imprimir:

42

extends

Uma classe pode herdar métodos e propriedades de outra classe usando a palavra-chave extends na declaração da classe. Não é possível herdar múltiplas classes; uma classe só pode herdar uma classe base.

Os métodos e propriedades herdados podem ser sobrescritos redeclarando-os com o mesmo nome definido na classe base. Entretanto, se o método foi definido na classe base como final esse método não poderá ser sobrescrito. É possível acessar os métodos sobrescritos ou propriedades estáticas referenciado-os com parent::.

Ao sobrescrever métodos, a assinatura de parâmetros deve permanecer a mesma ou o PHP gerará um erro de nível E_STRICT. Isto não se aplica ao construtor, que permite a sobrescrita com parâmetros diferentes.

Exemplo #8 Herança da Classe Simples

<?php
class ExtendClass extends SimpleClass
{
    
// Redefine o método pai
    
function displayVar()
    {
        echo 
"Classe Herdeira\n";
        
parent::displayVar();
    }
}

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

O exemplo acima irá imprimir:

Classe Herdeira
um valor padrão

::class

Desde o PHP 5.5, a palavra-chave class também pode ser utilizada para resolução de nome de classes. Pode-se obter uma string contendo o nome completo e qualificado da classe ClassName utilizando ClassName::class. Isso é particularmente útil em classes com namespaces.

Exemplo #9 Resolução de nome da classe

<?php
namespace NS {
    class 
ClassName {
    }

    echo 
ClassName::class;
}
?>

O exemplo acima irá imprimir:

NS\ClassName

Nota:

A resolução de nomes de classe através de ::class é uma transformação em tempo de compilação. Significando que a string com nome é criada antes que o autoloading tenha acontecido. Como consequência, os nomes de classe são expandidos mesmo que a classe não exista. Neste caso, nenhum erro será emitido.

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User Contributed Notes 21 notes

up
327
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"
?>
up
78
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
*/
?>
up
25
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.
up
31
wbcarts at juno dot com
8 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!
up
19
Notes on stdClass
7 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)
up
18
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.
up
21
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... ";
    }
}

?>
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9
moty66 at gmail dot com
7 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
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4
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.
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3
php at kingsquare dot nl
3 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!)
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5
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

?>
up
7
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 :)
up
3
the_french_cow at hotmail dot com
7 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.
up
-2
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)
up
-7
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.
up
-8
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 $this->className() is written two times in exactly the same way, the one contained in a new statement gets the className field and the other performs the actual method.
up
-9
ialsoagree
7 years ago
I think it's worth mentioning that if you define a function inside of an object method, that function cannot refer to "$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();
?>
up
-6
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()                                                                                                          
    {
...
up
-8
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.
up
-2
ohcc at 163 dot com
10 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;
?>
up
-17
alex c
7 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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