原文链接:http://tabalt.net/blog/php-traits/
PHP是单继承的语言,在PHP 5.4 Traits出现之前,PHP的类无法同时从两个基类继承属性或方法。php的Traits和Go语言的组合功能类似,通过在类中使用use关键字声明要组合的Trait名称,而具体某个Trait的声明使用trait关键词,Trait不能直接实例化。具体用法请看下面的代码:
<?php trait Drive { public $carName = 'trait'; public function driving() { echo "driving {$this->carName}\n"; } } class Person { public function eat() { echo "eat\n"; } } class Student extends Person { use Drive; public function study() { echo "study\n"; } } $student = new Student(); $student->study(); $student->eat(); $student->driving();
输出结果如下:
studyeatdriving trait
上面的例子中,Student类通过继承Person,有了eat方法,通过组合Drive,有了driving方法和属性carName。
如果Trait、基类和本类中都存在某个同名的属性或者方法,最终会保留哪一个呢?通过下面的代码测试一下:
<?php trait Drive { public function hello() { echo "hello drive\n"; } public function driving() { echo "driving from drive\n"; } } class Person { public function hello() { echo "hello person\n"; } public function driving() { echo "driving from person\n"; } } class Student extends Person { use Drive; public function hello() { echo "hello student\n"; } } $student = new Student(); $student->hello(); $student->driving();
输出结果如下:
hello studentdriving from drive
因此得出结论:当方法或属性同名时,当前类中的方法会覆盖 trait的 方法,而 trait 的方法又覆盖了基类中的方法。
如果要组合多个Trait,通过逗号分隔 Trait名称:
use Trait1, Trait2;
如果多个Trait中包含同名方法或者属性时,会怎样呢?答案是当组合的多个Trait包含同名属性或者方法时,需要明确声明解决冲突,否则会产生一个致命错误。
<?phptrait Trait1 { public function hello() { echo "Trait1::hello\n"; } public function hi() { echo "Trait1::hi\n"; }}trait Trait2 { public function hello() { echo "Trait2::hello\n"; } public function hi() { echo "Trait2::hi\n"; }}class Class1 { use Trait1, Trait2;}
输出结果如下:
PHP Fatal error: Trait method hello has not been applied, because there are collisions with other trait methods on Class1 in ~/php54/trait_3.php on line 20
使用insteadof和as操作符来解决冲突,insteadof是使用某个方法替代另一个,而as是给方法取一个别名,具体用法请看代码:
<?phptrait Trait1 { public function hello() { echo "Trait1::hello\n"; } public function hi() { echo "Trait1::hi\n"; }}trait Trait2 { public function hello() { echo "Trait2::hello\n"; } public function hi() { echo "Trait2::hi\n"; }}class Class1 { use Trait1, Trait2 { Trait2::hello insteadof Trait1; Trait1::hi insteadof Trait2; }}class Class2 { use Trait1, Trait2 { Trait2::hello insteadof Trait1; Trait1::hi insteadof Trait2; Trait2::hi as hei; Trait1::hello as hehe; }}$Obj1 = new Class1();$Obj1->hello();$Obj1->hi();echo "\n";$Obj2 = new Class2();$Obj2->hello();$Obj2->hi();$Obj2->hei();$Obj2->hehe();
输出结果如下:
Trait2::helloTrait1::hiTrait2::helloTrait1::hiTrait2::hiTrait1::hello
as关键词还有另外一个用途,那就是修改方法的访问控制:
<?php trait Hello { public function hello() { echo "hello,trait\n"; } } class Class1 { use Hello { hello as protected; } } class Class2 { use Hello { Hello::hello as private hi; } } $Obj1 = new Class1(); $Obj1->hello(); # 报致命错误,因为hello方法被修改成受保护的 $Obj2 = new Class2(); $Obj2->hello(); # 原来的hello方法仍然是公共的 $Obj2->hi(); # 报致命错误,因为别名hi方法被修改成私有的
Trait 也能组合Trait,Trait中支持抽象方法、静态属性及静态方法,测试代码如下:
<?phptrait Hello { public function sayHello() { echo "Hello\n"; }}trait World { use Hello; public function sayWorld() { echo "World\n"; } abstract public function getWorld(); public function inc() { static $c = 0; $c = $c + 1; echo "$c\n"; } public static function doSomething() { echo "Doing something\n"; }}class HelloWorld { use World; public function getWorld() { return 'get World'; }}$Obj = new HelloWorld();$Obj->sayHello();$Obj->sayWorld();echo $Obj->getWorld() . "\n";HelloWorld::doSomething();$Obj->inc();$Obj->inc();
输出结果如下:
HelloWorldget WorldDoing something12
原文链接:http://tabalt.net/blog/php-traits/

The article explains how to create, implement, and use interfaces in PHP, focusing on their benefits for code organization and maintainability.

The article discusses the differences between crypt() and password_hash() in PHP for password hashing, focusing on their implementation, security, and suitability for modern web applications.

Article discusses preventing Cross-Site Scripting (XSS) in PHP through input validation, output encoding, and using tools like OWASP ESAPI and HTML Purifier.

Autoloading in PHP automatically loads class files when needed, improving performance by reducing memory use and enhancing code organization. Best practices include using PSR-4 and organizing code effectively.

PHP streams unify handling of resources like files, network sockets, and compression formats via a consistent API, abstracting complexity and enhancing code flexibility and efficiency.

The article discusses managing file upload sizes in PHP, focusing on the default limit of 2MB and how to increase it by modifying php.ini settings.

The article discusses nullable types in PHP, introduced in PHP 7.1, allowing variables or parameters to be either a specified type or null. It highlights benefits like improved readability, type safety, and explicit intent, and explains how to declar

The article discusses the differences between unset() and unlink() functions in programming, focusing on their purposes and use cases. Unset() removes variables from memory, while unlink() deletes files from the filesystem. Both are crucial for effec


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

SublimeText3 Chinese version
Chinese version, very easy to use

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function
