Just a quick note that it's possible to declare visibility for multiple properties at the same time, by separating them by commas.
eg:
<?php
class a
{
protected $a, $b;
public $c, $d;
private $e, $f;
}
?>
The visibility of a property, a method or (as of PHP 7.1.0) a constant can be defined by prefixing
the declaration with the keywords public,
protected or
private. Class members declared public can be
accessed everywhere. Members declared protected can be accessed
only within the class itself and by inheriting and parent
classes. Members declared as private may only be accessed by the
class that defines the member.
Class properties may be defined as public, private, or protected. Properties declared without any explicit visibility keyword are defined as public.
Example #1 Property declaration
<?php
/**
* Define MyClass
*/
class MyClass
{
public $public = 'Public';
protected $protected = 'Protected';
private $private = 'Private';
function printHello()
{
echo $this->public;
echo $this->protected;
echo $this->private;
}
}
$obj = new MyClass();
echo $obj->public; // Works
echo $obj->protected; // Fatal Error
echo $obj->private; // Fatal Error
$obj->printHello(); // Shows Public, Protected and Private
/**
* Define MyClass2
*/
class MyClass2 extends MyClass
{
// We can redeclare the public and protected properties, but not private
public $public = 'Public2';
protected $protected = 'Protected2';
function printHello()
{
echo $this->public;
echo $this->protected;
echo $this->private;
}
}
$obj2 = new MyClass2();
echo $obj2->public; // Works
echo $obj2->protected; // Fatal Error
echo $obj2->private; // Undefined
$obj2->printHello(); // Shows Public2, Protected2, Undefined
?>Class methods may be defined as public, private, or protected. Methods declared without any explicit visibility keyword are defined as public.
Example #2 Method Declaration
<?php
/**
* Define MyClass
*/
class MyClass
{
// Declare a public constructor
public function __construct() { }
// Declare a public method
public function MyPublic() { }
// Declare a protected method
protected function MyProtected() { }
// Declare a private method
private function MyPrivate() { }
// This is public
function Foo()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate();
}
}
$myclass = new MyClass;
$myclass->MyPublic(); // Works
$myclass->MyProtected(); // Fatal Error
$myclass->MyPrivate(); // Fatal Error
$myclass->Foo(); // Public, Protected and Private work
/**
* Define MyClass2
*/
class MyClass2 extends MyClass
{
// This is public
function Foo2()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate(); // Fatal Error
}
}
$myclass2 = new MyClass2;
$myclass2->MyPublic(); // Works
$myclass2->Foo2(); // Public and Protected work, not Private
class Bar
{
public function test() {
$this->testPrivate();
$this->testPublic();
}
public function testPublic() {
echo "Bar::testPublic\n";
}
private function testPrivate() {
echo "Bar::testPrivate\n";
}
}
class Foo extends Bar
{
public function testPublic() {
echo "Foo::testPublic\n";
}
private function testPrivate() {
echo "Foo::testPrivate\n";
}
}
$myFoo = new Foo();
$myFoo->test(); // Bar::testPrivate
// Foo::testPublic
?>As of PHP 7.1.0, class constants may be defined as public, private, or protected. Constants declared without any explicit visibility keyword are defined as public.
Example #3 Constant Declaration as of PHP 7.1.0
<?php
/**
* Define MyClass
*/
class MyClass
{
// Declare a public constant
public const MY_PUBLIC = 'public';
// Declare a protected constant
protected const MY_PROTECTED = 'protected';
// Declare a private constant
private const MY_PRIVATE = 'private';
public function foo()
{
echo self::MY_PUBLIC;
echo self::MY_PROTECTED;
echo self::MY_PRIVATE;
}
}
$myclass = new MyClass();
MyClass::MY_PUBLIC; // Works
MyClass::MY_PROTECTED; // Fatal Error
MyClass::MY_PRIVATE; // Fatal Error
$myclass->foo(); // Public, Protected and Private work
/**
* Define MyClass2
*/
class MyClass2 extends MyClass
{
// This is public
function foo2()
{
echo self::MY_PUBLIC;
echo self::MY_PROTECTED;
echo self::MY_PRIVATE; // Fatal Error
}
}
$myclass2 = new MyClass2;
echo MyClass2::MY_PUBLIC; // Works
$myclass2->foo2(); // Public and Protected work, not Private
?>Objects of the same type will have access to each others private and protected members even though they are not the same instances. This is because the implementation specific details are already known when inside those objects.
Example #4 Accessing private members of the same object type
<?php
class Test
{
private $foo;
public function __construct($foo)
{
$this->foo = $foo;
}
private function bar()
{
echo 'Accessed the private method.';
}
public function baz(Test $other)
{
// We can change the private property:
$other->foo = 'hello';
var_dump($other->foo);
// We can also call the private method:
$other->bar();
}
}
$test = new Test('test');
$test->baz(new Test('other'));
?>The above example will output:
string(5) "hello" Accessed the private method.
Just a quick note that it's possible to declare visibility for multiple properties at the same time, by separating them by commas.
eg:
<?php
class a
{
protected $a, $b;
public $c, $d;
private $e, $f;
}
?>Beware: Visibility works on a per-class-base and does not prevent instances of the same class accessing each others properties!
<?php
class Foo
{
private $bar;
public function debugBar(Foo $object)
{
// this does NOT violate visibility although $bar is private
echo $object->bar, "\n";
}
public function setBar($value)
{
// Neccessary method, for $bar is invisible outside the class
$this->bar = $value;
}
public function setForeignBar(Foo $object, $value)
{
// this does NOT violate visibility!
$object->bar = $value;
}
}
$a = new Foo();
$b = new Foo();
$a->setBar(1);
$b->setBar(2);
$a->debugBar($b); // 2
$b->debugBar($a); // 1
$a->setForeignBar($b, 3);
$b->setForeignBar($a, 4);
$a->debugBar($b); // 3
$b->debugBar($a); // 4
?>Dynamic properties are "public".
<?php
class MyClass {
public function setProperty($value) {
$this->dynamicProperty = $value;
}
}
$obj = new MyClass();
$obj->setProperty('Hello World');
echo $obj->dynamicProperty; // Outputs "Hello World"
?>
This usage is the same as well:
<?php
class MyClass {
}
$obj = new MyClass();
$obj->dynamicProperty = 'Hello World';
echo $obj->dynamicProperty; // Outputs "Hello World"
?>if not overwritten, self::$foo in a subclass actually refers to parent's self::$foo
<?php
class one
{
protected static $foo = "bar";
public function change_foo($value)
{
self::$foo = $value;
}
}
class two extends one
{
public function tell_me()
{
echo self::$foo;
}
}
$first = new one;
$second = new two;
$second->tell_me(); // bar
$first->change_foo("restaurant");
$second->tell_me(); // restaurant
?>I couldn't find this documented anywhere, but you can access protected and private member varaibles in different instance of the same class, just as you would expect
i.e.
<?php
class A
{
protected $prot;
private $priv;
public function __construct($a, $b)
{
$this->prot = $a;
$this->priv = $b;
}
public function print_other(A $other)
{
echo $other->prot;
echo $other->priv;
}
}
class B extends A
{
}
$a = new A("a_protected", "a_private");
$other_a = new A("other_a_protected", "other_a_private");
$b = new B("b_protected", "ba_private");
$other_a->print_other($a); //echoes a_protected and a_private
$other_a->print_other($b); //echoes b_protected and ba_private
$b->print_other($a); //echoes a_protected and a_private
?>> Members declared protected can be accessed only within
> the class itself and by inherited classes. Members declared
> as private may only be accessed by the class that defines
> the member.
This is not strictly true. Code outside the object can get and set private and protected members:
<?php
class Sealed { private $value = 'foo'; }
$sealed = new Sealed;
var_dump($sealed); // private $value => string(3) "foo"
call_user_func(\Closure::bind(
function () use ($sealed) { $sealed->value = 'BAZ'; },
null,
$sealed
));
var_dump($sealed); // private $value => string(3) "BAZ"
?>
The magic lay in \Closure::bind, which allows an anonymous function to bind to a particular class scope. The documentation on \Closure::bind says:
> If an object is given, the type of the object will be used
> instead. This determines the visibility of protected and
> private methods of the bound object.
So, effectively, we're adding a run-time setter to $sealed, then calling that setter. This can be elaborated to generic functions that can force set and force get object members:
<?php
function force_set($object, $property, $value) {
call_user_func(\Closure::bind(
function () use ($object, $property, $value) {
$object->{$property} = $value;
},
null,
$object
));
}
function force_get($object, $property) {
return call_user_func(\Closure::bind(
function () use ($object, $property) {
return $object->{$property};
},
null,
$object
));
}
force_set($sealed, 'value', 'quux');
var_dump(force_get($sealed, 'value')); // 'quux'
?>
You should probably not rely on this ability for production quality code, but having this ability for debugging and testing is handy.I see we can redeclare private properties into child class
<?php
class A{
private int $private_prop = 4;
protected int $protected_prop = 8;
}
class B extends A{
private int $private_prop = 7; // we can redeclare private property!!!
public function printAll() {
echo $this->private_prop;
echo $this->protected_prop;
}
}
$b = new B;
$b->printAll(); // show 78
}
?>