我需要了解魔术函数__isset()
和普通函数isset()
的知识。实际上,PHP语言构造中isset()
和PHP魔术方法中__isset()
之间的真正区别是什么?当我在谷歌搜索时,他们说__isset()
是一个魔术函数。在PHP中,普通函数和魔术函数之间有哪些区别?
我需要了解魔术函数__isset()
和普通函数isset()
的知识。实际上,PHP语言构造中isset()
和PHP魔术方法中__isset()
之间的真正区别是什么?当我在谷歌搜索时,他们说__isset()
是一个魔术函数。在PHP中,普通函数和魔术函数之间有哪些区别?
isset()
这是一种语言结构,用于检查变量或类属性的初始化:
$a = 10;
isset($a); // true
isset($a, $b); // false
class Test
{
public $prop = 10;
}
$obj = new Test;
isset($obj->prop); // true
__isset()
这是一个魔术方法,当isset()
或empty()
检查不存在或无法访问的类属性时会被调用:
class Test
{
public function __isset($name) {
echo "Non-existent property '$name'";
}
}
$obj = new Test;
isset($obj->prop); // prints "Non-existent property 'prop'" and return false
isset() __isset()
语言结构 | 魔术方法 | 总是返回bool类型 | 结果取决于自定义逻辑* | 必须在代码中调用 | 由事件自动调用 | 可以有无限数量的参数 | 只有一个参数 | 可在任何范围内使用 | 必须定义为方法** | 是保留关键字 | 不是保留关键字 | 不能重新定义(解析错误) | 可以在扩展类中重新定义***
__isset()
的结果将自动转换为bool
。
实际上,您可以定义自定义函数__isset()
,但它与魔术方法无关。
请参见此示例。
与普通函数不同的是,魔术方法只能在类范围内定义,并在特定事件(如:无法访问的方法调用、类序列化、对无法访问的属性使用 unset()
等)自动调用。请参阅官方文档 重载。
__isset是一个魔术方法。魔术方法是内部调用的方法。
考虑以下代码:
<?php
// Declare a simple class
class TestClass
{
public $foo;
public function __construct($foo)
{
$this->foo = $foo;
}
public function __toString()
{
return $this->foo;
}
}
$class = new TestClass('Hello');
echo $class;
?>
这里的toString是一个神奇的方法,但你不需要直接调用它。当执行了echo $class;
这行代码时,PHP知道现在我应该把$class对象作为字符串来处理,并调用toString方法将任何对象转化为字符串(如果该类实现了该方法)。
所有魔术方法都是以这种间接的方式被调用。
下面是另一个例子:
<?php
class CallableClass
{
public function __invoke($x)
{
var_dump($x);
}
}
$obj = new CallableClass;
$obj(5);
var_dump(is_callable($obj));
?>
首先让我告诉你isset()函数的作用。
isset()函数检查值是否已经设置或是否为空。
isset()函数是PHP中的一个魔术方法。在PHP中,任何以“ _”开头的函数都是魔术方法。现在,当您在不可访问的属性上调用isset()或empty()时,将调用__isset(),也就是那些在类中未定义并在运行时被明确定义的属性。
以下是一段代码,应该可以让您更好地理解它:
<?php
class PropertyTest
{
/** Location for overloaded data. */
private $data = array();
/** Overloading not used on declared properties. */
public $declared = 1;
/** Overloading only used on this when accessed outside the class. */
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 ' . $trace[0]['line'],
E_USER_NOTICE);
return null;
}
/** As of PHP 5.1.0 */
public function __isset($name)
{
echo "Is '$name' set?\n";
return isset($this->data[$name]);
}
/** As of PHP 5.1.0 */
public function __unset($name)
{
echo "Unsetting '$name'\n";
unset($this->data[$name]);
}
/** Not a magic method, just here for example. */
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";
?>
简单来说,__isset()函数帮助isset()函数在类中工作时访问受保护/私有变量。
例如:
class test
{
public $x = array();
}
isset($test->x['key'])
来执行此操作。class test
{
protected $x = array();
function __isset($key)
{
return isset($this->x[$key]);
}
}
$x
是受保护的,您无法访问它,因此我们创建了__isset()
来帮助我们使用isset($x['key'])
您可以说__isset()
只是isset()
的桥梁。
isset()
的结果强制转换为bool
没有意义,因为它总是返回bool
。 - Alexander Yancharuk魔术方法是在某些事件发生时自动调用的函数。正常的函数必须由您的php代码特别调用。
在您的情况下:当您尝试获取一个不可访问的属性时,__isset()将自动被调用。
例如:
root@folgore:/tmp/php# cat a.php
<?php
class a {
private $att1;
public $att2;
function __isset($field) {
echo "__isset invoked for $field\n";
}
}
$obj=new a();
// __isset will be triggered:
isset($obj->att1);
// __isset will not be triggered:
isset($obj->att2);
root@folgore:/tmp/php# php a.php
__isset invoked for att1
isset()
是一个PHP函数。<?php
class PropertyTest
{
/** Location for overloaded data. */
private $data = array();
/** Overloading not used on declared properties. */
public $declared = 1;
/** Overloading only used on this when accessed outside the class. */
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 ' . $trace[0]['line'],
E_USER_NOTICE);
return null;
}
/* As of PHP 5.1.0 */
public function __isset($name)
{
echo "Is '$name' set?\n";
return isset($this->data[$name]);
}
/** As of PHP 5.1.0 */
public function __unset($name)
{
echo "Unsetting '$name'\n";
unset($this->data[$name]);
}
/** Not a magic method, just here for example. */
public function getHidden()
{
return $this->hidden;
}
}
echo "<pre>\n";
$obj = new PropertyTest;
//__set() is called when 'a' property is not visible outside of class
$obj->a = 1;
//__get() is called when 'a' property is not visible outside of class
echo "a: ".$obj->a . "\n\n";
//__isset() is called when 'a' property is not visible outside of class
var_dump(isset($obj->a));
unset($obj->a);
//__isset() is called when 'a' property is not visible outside of class
var_dump(isset($obj->a));
echo "\n";
//__isset() is not called as 'declared' property is visible outside of class
var_dump(isset($obj->declared));
//__get() is not called as 'declared' property is visible outside of class
echo "declared: ". $obj->declared . "\n\n";
//__set() is not called as 'declared' property is visible outside of class
$obj->declared = 3;
//__get() is not called as 'declared' property is visible outside of class
echo "declared: ". $obj->declared . "\n\n";
//__isset() is called as 'hidden' property is not visible outside of class
var_dump(isset($obj->hidden));
echo "Let's experiment with the private property named 'hidden':\n";
echo "Privates are visible inside the class, so __get() not used...\n";
echo $obj->getHidden() . "\n";
echo "Privates not visible outside of class, so __get() is used...\n";
var_dump($obj->hidden);
?>
Setting 'a' to '1'
Getting 'a'
a: 1
Is 'a' set?
bool(true)
Unsetting 'a'
Is 'a' set?
bool(false)
bool(true)
declared: 1
declared: 3
Is 'hidden' set?
bool(false)
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'
NULL
isset()
用于变量,而 __isset()
用于类的属性。
__isset
?_isset
并不存在于原生语言中。如果是的话,可以在谷歌上搜索第一个结果:http://www.php.net/manual/en/language.oop5.overloading.php 。__isset()
会在调用不可访问属性的isset()
或empty()
时被触发。 - Felix Klingisset()
和_isset()
有什么区别? - Lal krishnan S Lisset()
不是一个函数,而是一种语言结构。 - Syjin