How to use PHP INSTANCEOF

The instanceof operator is introduced in PHP 5. Is_a () was used before, but is_a () is outdated. It is best to use instanceof.

1. Used to determine whether a variable belongs to an instance of a class;

2. It is used to determine whether a variable is an instance that inherits the subclass of a parent class;

3. It is used to determine whether a variable is an instance of an object that implements an interface.

Before PHP 5.1.0, if the class name to be checked does not exist, instanceof will call _ autoload (). In addition, a fatal error occurs if the class is not loaded. You can avoid this problem by using dynamic class reference or using a string variable containing the class name:

The following example illustrates the usage of php instanceof:

If (! Empty ($ current_user )){
If ($ current_user instanceof WP_User)
Return;
 
// Upgrade stdClass to WP_User
If (is_object ($ current_user) & isset ($ current_user-> ID )){
$ Cur_id = $ current_user-> ID;
$ Current_user = null;
Wp_set_current_user ($ cur_id );
Return;
 }
 
// $ Current_user has a junk value. Force to WP_User with ID 0.
$ Current_user = null;
Wp_set_current_user (0 );
Return false;
}

For example, in the highlighted part of the code, if ($ current_user instanceof WP_User), WP_User is a class name. Here, this sentence is used to determine whether $ current_user is an instance of the WP_User class. That is, to determine whether $ current_user = new WP_User () exists in the previous code ().

Use the instanceof keyword to determine whether an object is an instance of a class or a subclass of a class, or whether it implements a specific interface and performs corresponding operations.

Example #6 avoid class name searches and fatal errors caused by instanceof in PHP 5.0

<? Php
$ D = 'notmyclass ';
Var_dump ($ a instanceof $ d); // no fatal error here
?>

Code format: instance name instanceof class name

Use of the instanceof operator

The following example can be run.

<?
Class User {
Private $ name;
Public function getName (){
Return "UserName is". $ this-> name;
 }
}
Class NormalUser extends User {
Private $ age = 99;
Public function getAge (){
Return "age is". $ this-> age;
 }
}
Class UserAdmin {// operation.
Public static function getUserInfo (User $ _ user ){
Echo $ _ user-> getAge ();
 }
}
$ NormalUser = new NormalUser ();
UserAdmin: getUserInfo ($ normalUser );
?>

Program running result:

Age is 99

In the User class, the following error is reported because this method is not available:

<?
Class User {
Private $ name;
Public function getName (){
Return "UserName is". $ this-> name;
 }
}
Class NormalUser extends User {
Private $ age = 99;
Public function getAge (){
Return "age is". $ this-> age;
 }
}
Class UserAdmin {// operation.
Public static function getUserInfo (User $ _ user ){
Echo $ _ user-> getAge ();
 }
}
$ User = new User (); // Here new is User.
UserAdmin: getUserInfo ($ User );
?>

Program running result:

Fatal error: Call to undefined method User: getAge () in E: \ PHPProjects \ NowaMagic \ php \ php_InstanceofOperator.php on line 99

Use the instatnceof operator to ensure code security

Use the instatnceof operator to determine the type before the operation. To ensure code security.

<?
Class User {
Private $ name;
Public function getName (){
Return "UserName is". $ this-> name;
 }
}
Class NormalUser extends User {
Private $ age = 99;
Public function getAge (){
Return "age is". $ this-> age;
 }
}
Class UserAdmin {// operation.
Public static function getUserInfo (User $ _ user ){
If ($ _ user instanceof NormalUser ){
Echo $ _ user-> getAge ();
} Else {
Echo "the type is incorrect. You cannot use this method .";
  }
 }
}
$ User = new User (); // Here new is User.
UserAdmin: getUserInfo ($ User );
?>

Program running result:

The type is incorrect. You cannot use this method.

This is the usage of the php keyword instanceof.