PHP--Magic method, magic constant Simple Introduction

Magic Method:

PHP treats all the methods in the class that begin with __ (two underscores) as a magic method, and it is generally recommended that users do not prefix the custom method with __. Magic Method:

1. __construct ()

The default constructor method for a class, if __construct () and a method with the same name as the class, is called by default __construct () instead of the same name method. In general, the user-defined construction method will also use __construct ().

2. __destruct ()

A destructor for a class that executes when all references to the object are deleted, or when an object is explicitly destroyed.

3. __get ($name)

Can be summed up as: When reading an object's properties in a $object->a way, if property a exists and is public, the value of the property is returned directly, and if the property A does not exist or is a type that is not directly accessible by protected/private, it will be called __ The Get ($name) method, whichever is the return value. You can generally use this method to allow externally restricted access to internal properties, or to perform reflection operations similar to those in Java.

4. __set ($name, $value)

Similar to __get ($name), when assigning a value to a property in the form of $object->a = 17, if property a exists and is public, then the property A is assigned directly to it, and if the property A does not exist or is a protected/private type, it will be called __ Set ($name, $value) method.

5. __call ($name, $arguments)/ __callstatic ($name, $arguments)

The __call ($name, $arguments) method is called when a method that does not exist or is not accessible is called. The __callstatic ($name, $arguments) method is called when a non-existent or inaccessible method is called in a static method.

6. __tostring ()

It is called directly when the object is printed. such as Echo $object;

7. __clone ()

Called directly when the object is copied. such as $ A = new Action (); $a = $object;

8. __isset ($name)/__unset ($name)

When you use Isset () or empty () for a property that does not exist or is not accessible, __isset () is called, and __unset () is called when unset a nonexistent or inaccessible property, otherwise the attribute is directly unset.

9. __set_state ()

When an object is output with Var_export (), __set_state () is called, and the output is based on the return value of the Magic method. Note: Var_export () is similar to Var_dump (), except that the contents of the Var_export () output conform to the PHP syntax. Note how to use:

$test=NewTest ();$b=Var_export($test,true);Var_dump($b);classTest { Public $a;  Public Static function__set_state ($array) {        $ab=NewTest (); $ab->a = 10; return $ab; }}

__autoload ($name)

When an object is instantiated, the method is called if the corresponding class does not exist. Note: The method is a global function, and the parameter is the name of the class.

__sleep ()/__wakup ()

Slightly.

Magic constants:

1. __line__

Returns the current line number in the file.

<span style="font-size:18px; "><? "". __line__. " Line "  "<br/>";? ></span>

2. __file__

Returns the full path of the file in which it resides. Include file name

<span style="font-size:18px; "><?  "" <br/> ";?" ></span>

3. __function__

Returns the name of the function being located.

<span style="font-size:18px; "><? phpfunction Test () {echo  " This function is named:""<br/> ";} Test ();? ></span>

4. __class__

Returns the name of the class in which it is located.

<span style="font-size:18px;"><?PHPclassTest {function Show () {echo"the class name is:". __class__."<br>"; Echo"the function is named:". __function__; Echo"<br/>";}} $t=Newtest (); $t-Show ();?></span>

5. __method__

Returns the name of the class method in which it is located. Note that __method__ returns the form of "class::function", while __function__ returns the form of "function".

6.__dir__

Returns the directory where the file resides. If used in the included file, returns the directory where the included files are located. It is equivalent to dirname (__file__). Unless it is a root directory, the name in the directory does not include the trailing slash. Does not contain a file name. (New in PHP 5.3.0) =

<span style="font-size:18px; "><? "". __dir__. " folder under "  "<br/>";? ></span>

7.__namespace__

The name of the current namespace (case-sensitive). This constant is defined at compile time (PHP 5.3.0 is new).

8.__trait__

Trait's name (PHP 5.4.0 new Plus). From PHP 5.4 This constant returns the name of the trait when it is defined (case-sensitive). The Trait name includes its declared function area (for example, Foo\bar).

PHP--Magic method, magic constant Simple introduction