Introduction to PHP magic constants and summary of magic function usage code instructions

Magic Constant

1. LINE
Returns the current line number in the file.

2. FILE
Returns the full path and file name of the file. If used in an include file, returns the include file name. As of PHP 4.0.2, FILE always contains an absolute path, while versions before that sometimes contained a relative path.

3. FUNCTION
Returns the function name (newly added in PHP 4.3.0). Since PHP 5 this constant returns the name of the function as it was defined (case sensitive). In PHP 4 this value is always lowercase.

4. CLASS
Returns the name of the class (newly added in PHP 4.3.0). Since PHP 5 this constant returns the name of the class when it was defined (case sensitive). In PHP 4 this value is always lowercase.

5. METHOD
Returns the method name of the class (newly added in PHP 5.0.0). Returns the name of the method as it was defined (case-sensitive).

What is a magic function?

The functions at the beginning are named magic functions. Such functions are triggered under specific conditions. For example: set() get(), etc.
are triggered when setting or getting non-existing properties.
What magic functions are there?
In general, there are the following magic functions
construct() destruct() get() set() isset() unset() call() callStatic()
sleep() wakeup() toString() set_state() clone() autoload()
construct() When instantiating an object, this method of the object is first called.
destruct() This method is called when deleting an object or when the object operation terminates.

class test1 { 
public function construct() { 
var_dump(function); 
} 
public function destruct() { 
var_dump(function); 
} 
} 
$t1 = new test1 ; 
unset($t1);

get is called when trying to read a property that does not exist.
set is called when trying to write a value to a property that does not exist.
isset is called when trying to detect a property that does not exist.
unset is called when trying to unset a property that does not exist.

class test2 { 
public $name3; 
public function set($key, $value) { 
var_dump(function. ' 
KEY:' 
.$key.' 
Value:' 
.$value); 
} 
public function get($key) { 
var_dump(function. 'KEY:'.$key); 
} 
public function isset($key) { 
var_dump(function. ' KEY:'.$key); 
} 
public function unset($key) { 
var_dump(function. ' KEY:'.$key); 
} 
} 
$t =new test2 ; 
$t->name = "steven"; 
$t->name2; 
$t->name3; 
isset($t->name2); 
isset($t->name3); 
unset($t->name4);

sleep is called when serializing objects
wakeup is called when deserializing objects
One thing to note:
1. sleep() must return an array or object (usually returns is $this), the returned value will be used as the serialized
value.
If this value is not returned, serialization fails. This also means that deserialization will not trigger the wakeup event.
2. Serialization will save the attributes assigned by default. If you want to assign the content by instantiation, you need to specify the attribute in the array returned by sleep().
For example, the difference between $id and $id2.

class test3 { 
public $name = "steven"; 
public $id = "1"; public $id2; 
public function sleep() { 
var_dump(function); // 序列化不成功.没有返回值.反序列也失败 // 
return array("name"); // 序列化成功.有返回值.反序列成功.id2属性能被恢复 // 
return array("name", "id2");// 序列化成功.有返回值.反序列成功.id2属性不能被恢复 
return array("name"); } 
public function testEcho() { 
var_dump($this->name); 
var_dump($this->id); 
var_dump($this->id2); 
} 
public function wakeup() { 
var_dump(function); 
$this->testEcho(); 
} 
} 
$t3= new test3 ; 
$t3->id2 = uniqid(); 
$t3s = serialize($t3); 
unserialize($t3s);

toString When printing an object directly, this method will be called

class test4 { 
public function toString() { 
return "toString"; 
} 
} 
$t4 = new test4(); 
echo $t4; 
print $t4; 
var_dump($t4); 
print_r($t4);

call($func, $param) When trying to call a method that does not exist Called.
This method must have two parameters, the first is the name of the called method, and the second is a parameter array of the called method.
It should be noted that when you call the private method of the parent class in a subclass, or call the non-protected method of the class in an instance, call() will not be called

class test5 { 
public function call($func, $param) { 
var_dump('Function:'.$func); 
var_dump($param); 
} 
} 
$t5 = new test5; 
$t5->echoTest('xx','xx','xx');

callStatic() is called when trying to call a non-existent

static
method This method must have two parameters, the first is the name of the method to be called, the second Is an array of parameters for the called method. Appears in PHP5.3

class test51 { 
public function callStatic($fun, $param) { 
var_dump('Function:'.$func); 
var_dump($param); 
} 
} 
test51::test('xx','xx','xx');

set_state() is called when using var_export to export an instance. This method has a parameter that contains all the member attributes of the exported instance. An array

class test6 { 
public function set_state($arr){ 
var_dump($arr); 
} 
} 
$t6 = new test6; 
$t6->age = "12"; 
var_export($t6, true); 
var_export($t6); 
eval(' 
$b=' 
.var_export($t6,true).';'); 
print_r($b);

clone() is called when cloning an instance.
Note:

1. In php5, assignments between objects are always passed by address reference.

2 .If you want to pass it as an actual value, you need to use the clone keyword
3.Clone is only an instance. If a member attribute in the instance is also an instance, then this member attribute will still be
passed to the new instance using the reference method.
// Assignments between objects are always passed by address reference. The age attributes of $t71 $t72 are the same.

class test71 { 
public $age = 10; 
} 
$t71 = new test71(); 
$t72 = $t71 ; 
var_dump($t71->age) ; 
$t71->age =12 ; 
var_dump($t71->age) ; 
var_dump($t72->age) ; // 如果要以实际值来传递，则需要用到clone关键词 $t73 = clone $t71; $t71->age = 13 ; var_dump($t71->age) ; 
var_dump($t73->age) ; // 如果实例中的某个成员属性也是个实例，那么这个成员属性还是会以引用方法被传递到新的实例。

autoload() function. When creating an instantiation, if If the corresponding class does not exist, it will be called

function autoload($class) { 
　　 if ( $class == "test8" ){ 
require_once
 
dirname
(FILE).'/class8.php';  
} 
} 
spl_autoload(); 
$t8 = new test8; 
var_dump($t8->age);

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