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;
}
?>
对属性或方法的访问控制（PHP 7.1.0 以后支持常量），是通过在前面添加关键字
public（公有），protected（受保护）或
private（私有）来实现的。被定义为公有的类成员可以在任何地方被访问。
被定义为受保护的类成员则可以被其自身以及其子类和父类访问。被定义为私有的类成员则只能被其定义所在的类访问。
类属性可以定义为public， private 或者 protected。在没有任何访问控制关键字的情况下，属性声明为 public。
示例 #1 属性声明
<?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; // 这行能被正常执行
echo $obj->protected; // 这行会产生一个致命错误
echo $obj->private; // 这行也会产生一个致命错误
$obj->printHello(); // 输出 Public、Protected 和 Private
/**
* Define MyClass2
*/
class MyClass2 extends MyClass
{
// 可以对 public 和 protected 进行重定义，但 private 而不能
public $public = 'Public2';
protected $protected = 'Protected2';
function printHello()
{
echo $this->public;
echo $this->protected;
echo $this->private;
}
}
$obj2 = new MyClass2();
echo $obj2->public; // 这行能被正常执行
echo $obj2->protected; // 这行会产生一个致命错误
echo $obj2->private; // 未定义 private
$obj2->printHello(); // 输出 Public2、Protected2 和 Undefined
?>
从 PHP 8.4 开始，属性也可以设置不对称的可见性，读取（get）
和写入（set）可以有不同的范围。
具体来说，可以单独指定set可见性，只要它不比默认可见性更宽。
示例 #2 不对称属性可见性
<?php
class Book
{
public function __construct(
public private(set) string $title,
public protected(set) string $author,
protected private(set) int $pubYear,
) {}
}
class SpecialBook extends Book
{
public function update(string $author, int $year): void
{
$this->author = $author; // OK
$this->pubYear = $year; // Fatal Error
}
}
$b = new Book('How to PHP', 'Peter H. Peterson', 2024);
echo $b->title; // Works
echo $b->author; // Works
echo $b->pubYear; // Fatal Error
$b->title = 'How not to PHP'; // Fatal Error
$b->author = 'Pedro H. Peterson'; // Fatal Error
$b->pubYear = 2023; // Fatal Error
?>关于不对称可见性有一些注意事项：
set可见性。
set 可见性必须和 get 可见性相同或更严格。
也就是说，public protected(set) 和 protected protected(set)
是允许的，但是 protected public(set) 会导致语法错误。
public，那么主要可见性可能被省略。
也就是说，public private(set) 和 private(set)
会有相同的结果。
private(set) 可见性会自动变为 final，
并且不能在子类中重新声明。
set 可见性，而不是 get。
这是因为引用可能用于修改属性值。
get 和 set 操作，
因此会遵循 set 可见性，因为这总是更严格的。
当一个类继承另一个类时，子类可以重新定义任何不是 final 的属性。
这样做时，可以扩大主要可见性或 set 可见性，只要新的可见性和父类相同或更宽。
但是要注意，如果一个 private 属性被重写，它实际上并没有改变父类的属性，
而是创建了一个具有不同内部名称的新属性。
示例 #3 不对称属性继承
<?php
class Book
{
protected string $title;
public protected(set) string $author;
protected private(set) int $pubYear;
}
class SpecialBook extends Book
{
public protected(set) $title; // OK, as reading is wider and writing the same.
public string $author; // OK, as reading is the same and writing is wider.
public protected(set) int $pubYear; // Fatal Error. private(set) properties are final.
}
?>类中的方法可以被定义为 public、private 或 protected。如果没有设置这些关键字，则该方法默认为 public。
示例 #4 方法声明
<?php
/**
* Define MyClass
*/
class MyClass
{
// 声明一个公有的构造函数
public function __construct() { }
// 声明一个公有的方法
public function MyPublic() { }
// 声明一个受保护的方法
protected function MyProtected() { }
// 声明一个私有的方法
private function MyPrivate() { }
// 此方法为公有
function Foo()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate();
}
}
$myclass = new MyClass;
$myclass->MyPublic(); // 这行能被正常执行
$myclass->MyProtected(); // 这行会产生一个致命错误
$myclass->MyPrivate(); // 这行会产生一个致命错误
$myclass->Foo(); // 公有，受保护，私有都可以执行
/**
* Define MyClass2
*/
class MyClass2 extends MyClass
{
// 此方法为公有
function Foo2()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate(); // 这行会产生一个致命错误
}
}
$myclass2 = new MyClass2;
$myclass2->MyPublic(); // 这行能被正常执行
$myclass2->Foo2(); // 公有的和受保护的都可执行，但私有的不行
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
?>PHP 7.1.0 开始，类的常量可以定义为 public、private 或 protected。如果没有设置这些关键字，则该常量默认为 public。
示例 #5 PHP 7.1.0 中的常量声明
<?php
/**
* Define MyClass
*/
class MyClass
{
// 公有常量
public const MY_PUBLIC = 'public';
// 受保护的常量
protected const MY_PROTECTED = 'protected';
// 私有常量
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; // 这行可以正常执行
MyClass::MY_PROTECTED; // 这行会产生一个致命错误
MyClass::MY_PRIVATE; // 这行会产生一个致命错误
$myclass->foo(); // 将会输出：Public Protected Private
/**
* Define MyClass2
*/
class MyClass2 extends MyClass
{
// This is public
function foo2()
{
echo self::MY_PUBLIC;
echo self::MY_PROTECTED;
echo self::MY_PRIVATE; // 这行会产生一个致命错误
}
}
$myclass2 = new MyClass2;
echo MyClass2::MY_PUBLIC; // 这行可以正常执行
$myclass2->foo2(); // 将会输出：Public Protected，MY_PRIVATE 是私有常量，无法输出
?>同一个类的对象即使不是同一个实例也可以互相访问对方的 private 与 protected 成员。 这是由于在这些对象的内部具体实现的细节都是已知的。
示例 #6 访问同一个对象类型的 private 成员
<?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)
{
// 我们可以改变 private 属性：
$other->foo = 'hello';
var_dump($other->foo);
// 我们也可以调用 private 方法：
$other->bar();
}
}
$test = new Test('test');
$test->baz(new Test('other'));
?>以上示例会输出：
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, $f;
}
?>Dynamic properties are "public".
<?php
class MyClass {
public function setProperty($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
?>> 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 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
?>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
}
?>