Magic in PHP: __construct ,__ destruct ,__ call ,__ callStatic ,__ get ,__ set ,__ isset ,__ unset ,__ sleep,

Source: Internet
Author: User
Tags autoload
1. The _ get and _ set methods are designed for attributes that are not declared in the class and their parent class: __get ($ property) this method is called when an undefined property is called; __ set ($ property, $ value) assigns & amp; 20540 to an undefined property.

1. _ get, _ set

These two methods are designed for attributes that are not declared in the class and their parent class:

_ Get ($ property) access this method when an undefined property is called;

_ Set ($ property, $ value) is called when an undefined attribute is assigned a value;

Here, there is no declaration that the access control is "proteced" and "private" when an object is called (that is, an attribute with no access permission ).

2. _ isset and _ unset

_ Isset ($ property) this method is called when the isset () function is called on an undefined property;

_ Unset ($ property) this method is called when the unset () function is called on an undefined property;

Similar to the _ get method and _ set method, there is no declaration here, including the access control for the proteced and private attributes when the object is called (that is, the attribute with no access permission ).

3. _ call

_ Call ($ method, $ arg_array) this method is called when an undefined method is called.

The undefined method here includes methods with no access permission.

4. _ autoload

_ Autoload function, which is automatically called when trying to use a class that has not been defined. By calling this function, the script engine has the last chance to load the required class before a PHP error fails.

Note: The Exception thrown in the _ autoload function cannot be caught by the catch statement block and cause a fatal error.

5. _ construct and _ destruct

_ Construct constructor: This method is called when an object is created. the advantage of this method is that the constructor has a unique name, no matter what the name of the class is. In this way, you do not need to change the name of the constructor when changing the class name.

_ Destruct destructor. PHP will call this method before the object is destroyed (that is, before it is cleared from the memory. By default, PHP only releases the memory occupied by object attributes and destroys object-related resources. The Destructor allows you to execute arbitrary code to clear the memory after using an object. When PHP decides that your script is no longer related to objects, the destructor will be called. In the namespace of a function, this occurs when the function returns.

For global variables, this occurs at the end of the script. If you want to explicitly destroy an object, you can assign any other value to the variable pointing to the object. Usually, the variable value is NULL or unset is called.

6. _ clone

Object assignment in PHP5 is a reference assignment. if you want to copy an object, you need to use the clone method. when you call this method, the object will automatically call the _ clone magic method, if you need to perform some initialization operations on object replication, you can implement them in the _ clone method.

7. _ toString

The _ toString method is automatically called when an object is converted to a string. for example, if the class does not implement this method when echo is used to print the object, the object cannot be printed by echo. Otherwise, the following information is displayed:

Catchable fatal error: Object of class test cocould not be converted to string in

This method must return a string

Before PHP 5.2.0, the __tostring method takes effect only when echo () or print () is used in combination. PHP 5.2.0 and later can take effect in any string environment (for example, using the % s modifier through printf (), but cannot be used in non-string environment (for example, using the % d modifier ). From PHP 5.2.0, if an undefined _ toString method object is converted to a string, an E_RECOVERABLE_ERROR error is returned.

8. _ sleep and _ wakeup

_ Used for sleep serialization;

_ Called when wakeup is deserialized;

Serialize () checks whether the class has a function named _ sleep. In this case, the function will run before any serialization. It can clear the object and should return an array containing all variable names to be serialized in the object.

The purpose of _ sleep is to close any database connection that an object may have, submit data in waiting or perform similar cleanup tasks. In addition, this function is useful if a very large object does not need to be fully stored.

Conversely, unserialize () checks the existence of a function with the magic name _ wakeup. If yes, this function can reconstruct any resources that an object may have. _ Wakeup is used to reconstruct any database connections that may be lost during serialization and process other re-initialization tasks.

9. _ set_state

When var_export () is called, this static method is called (effective from PHP 5.1.0 ).

The unique parameter of this method is an array, which contains values by array ('properties' => value ,...) Class attributes in the format.

10. _ invoke

When you try to call an object by calling a function, the __invoke method is automatically called. PHP5.3.0 or later is valid.

11. _ callStatic

It works in a way similar to the _ call () magic method, __callstatic () is used to handle static method calls, which is effective in PHP5.3.0 or later versions.

PHP does enhance the definition of the _ callStatic () method. it must be public and declared as static. Similarly, the __call () magic method must be defined as public, and all other magic methods must be.

PHP official magic method introduction:

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