PHP instanceof operator _php Tutorial for enforcing object types

First, Introduction

Enforcing object types in PHP, which is now a mainstream development language , can sometimes be very important. If it is missing, or because it lacks this knowledge-based on incorrect programming assumptions, or simply because of laziness, you will see results that you do not want in a particular Web application. Especially when programming with PHP(which is now the mainstream development language) 4, it is very easy to use the "is_a ()" function (although there are other methods) to verify the type of object you are using. There is no doubt that forcing object types can also be used to filter input objects (which need to be passed as parameters to other PHP in the same application(as the current mainstream development language) Class).

However, PHP(which is now the mainstream development language) 4 does not expose some of the weaknesses of its object model-in order to implement some of the features that appear in a mature object-oriented language, it may occasionally require additional code to be written. For a long time, this fact has been known as the community of PHP, which is now the mainstream development language . However, with the release of PHP(which is now the mainstream development language) 5, many of these extremely valuable features are added as part of an improved object model. They will help you more closely implement object-based code development-allowing you to use specific object features.

In the above case, you should pay special attention when it comes to object type coercion. In fact, during the execution of a Web application, PHP(as the current mainstream development language) 5 provides developers with at least two ways to examine object types--they are the "instanceof" operator and the "type hint" feature. Now go to the topic of this article, I will introduce the use of PHP(as the current mainstream development language) 5 "instanceof" operator; you will soon find that it can be very handy to determine if the object you are using belongs to a particular type.

This article will use some object-oriented examples to help you understand how to implement mandatory object types in PHP 5, whichis now a mainstream development language .

Two, you shouldn't do what

To demonstrate how to implement object type coercion in PHP(as the current mainstream development language) 5, I will use the (X) HTML widget class, as well as a simple page builder class, and make simple modifications to PHP(as the current mainstream development language) 5 development environment.

My first example enumerates some of the (X) HTML widget classes derived from an abstract base class "HtmlElement", which skips checks to their input object types. Please look at the following classes first:

Defines the abstract class Htmlelementabstract class htmlelement{protected $attributes; protected function __construct ($attributes) {if (!　　Is_array ($attributes)) {throw new Exception (Invalid attribute type);　} $this->attributes= $attributes; }//abstract gethtml () method abstractly protected function gethtml ();} Defines the specific class div-extension Htmlelementclass Div extends htmlelement{private $output =
  
   data= $data; The specific implementation of the//gethtml () method
  

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