Community Learn Tools Library Leisure
search
English
Home > Backend Development > PHP Tutorial > PHP learning--Traits new features, php--traits new features_PHP tutorial

PHP learning--Traits new features, php--traits new features_PHP tutorial

WBOY
Release： 2016-07-13 10:11:39
Original
890 people have browsed it

PHP的学习--Traits新特性，php--traits新特性

在阅读yii2源码的时候接触到了trait，就学习了一下，写下博客记录一下。

自 PHP 5.4.0 起，PHP 实现了代码复用的一个方法，称为 traits。

Traits 是一种为类似 PHP 的单继承语言而准备的代码复用机制。Trait 为了减少单继承语言的限制，使开发人员能够自由地在不同层次结构内独立的类中复用方法集。Traits 和类组合的语义是定义了一种方式来减少复杂性，避免传统多继承和混入类（Mixin）相关的典型问题。

Trait 和一个类相似，但仅仅旨在用细粒度和一致的方式来组合功能。Trait 不能通过它自身来实例化。它为传统继承增加了水平特性的组合；也就是说，应用类的成员不需要继承。

Trait 示例

<?<span>php
trait ezcReflectionReturnInfo {
    </span><span>function</span> getReturnType() { <span>/*</span><span>1</span><span>*/</span><span> }
    </span><span>function</span> getReturnDescription() { <span>/*</span><span>2</span><span>*/</span><span> }
}

</span><span>class</span> ezcReflectionMethod <span>extends</span><span> ReflectionMethod {
    </span><span>use</span><span> ezcReflectionReturnInfo;
    </span><span>/*</span><span> ... </span><span>*/</span><span>
}

</span><span>class</span> ezcReflectionFunction <span>extends</span><span> ReflectionFunction {
    </span><span>use</span><span> ezcReflectionReturnInfo;
    </span><span>/*</span><span> ... </span><span>*/</span><span>
}
</span>?>
Copy after login

优先级

从基类继承的成员被 trait 插入的成员所覆盖。优先顺序是来自当前类的成员覆盖了 trait 的方法，而 trait 则覆盖了被继承的方法。

优先顺序示例

<?<span>php
</span><span>class</span><span> Base {
    </span><span>public</span> <span>function</span><span> sayHello() {
        </span><span>echo</span> 'Hello '<span>;
    }
}

trait SayWorld {
    </span><span>public</span> <span>function</span><span> sayHello() {
        parent</span>::<span>sayHello();
        </span><span>echo</span> 'World!'<span>;
    }
}

</span><span>class</span> MyHelloWorld <span>extends</span><span> Base {
    </span><span>use</span><span> SayWorld;
}

</span><span>$o</span> = <span>new</span><span> MyHelloWorld();
</span><span>$o</span>-><span>sayHello();
</span>?>
Copy after login

以上例程会输出：Hello World!

从基类继承的成员被插入的 SayWorld Trait 中的 sayHello 方法所覆盖。其行为 MyHelloWorld 类中定义的方法一致。优先顺序是当前类中的方法会覆盖 trait 方法，而 trait 方法又覆盖了基类中的方法。

另一个优先级顺序的例子

<?<span>php
trait HelloWorld {
    </span><span>public</span> <span>function</span><span> sayHello() {
        </span><span>echo</span> 'Hello World!'<span>;
    }
}

</span><span>class</span><span> TheWorldIsNotEnough {
    </span><span>use</span><span> HelloWorld;
    </span><span>public</span> <span>function</span><span> sayHello() {
        </span><span>echo</span> 'Hello Universe!'<span>;
    }
}

</span><span>$o</span> = <span>new</span><span> TheWorldIsNotEnough();
</span><span>$o</span>-><span>sayHello();
</span>?>
Copy after login

以上例程会输出：Hello Universe!

多个 trait

通过逗号分隔，在 use 声明列出多个 trait，可以都插入到一个类中。

多个 trait 的用法的例子

<?<span>php
trait Hello {
    </span><span>public</span> <span>function</span><span> sayHello() {
        </span><span>echo</span> 'Hello '<span>;
    }
}

trait World {
    </span><span>public</span> <span>function</span><span> sayWorld() {
        </span><span>echo</span> 'World'<span>;
    }
}

</span><span>class</span><span> MyHelloWorld {
    </span><span>use</span> Hello,<span> World;
    </span><span>public</span> <span>function</span><span> sayExclamationMark() {
        </span><span>echo</span> '!'<span>;
    }
}

</span><span>$o</span> = <span>new</span><span> MyHelloWorld();
</span><span>$o</span>-><span>sayHello();
</span><span>$o</span>-><span>sayWorld();
</span><span>$o</span>-><span>sayExclamationMark();
</span>?>
Copy after login

以上例程会输出：Hello World!

冲突的解决

如果两个 trait 都插入了一个同名的方法，如果没有明确解决冲突将会产生一个致命错误。

为了解决多个 trait 在同一个类中的命名冲突，需要使用 insteadof 操作符来明确指定使用冲突方法中的哪一个。

以上方式仅允许排除掉其它方法，as 操作符可以将其中一个冲突的方法以另一个名称来引入。

冲突解决的例子

<?<span>php
trait A {
    </span><span>public</span> <span>function</span><span> smallTalk() {
        </span><span>echo</span> 'a'<span>;
    }
    </span><span>public</span> <span>function</span><span> bigTalk() {
        </span><span>echo</span> 'A'<span>;
    }
}

trait B {
    </span><span>public</span> <span>function</span><span> smallTalk() {
        </span><span>echo</span> 'b'<span>;
    }
    </span><span>public</span> <span>function</span><span> bigTalk() {
        </span><span>echo</span> 'B'<span>;
    }
}

</span><span>class</span><span> Talker {
    </span><span>use</span> A,<span> B {
        B</span>::<span>smallTalk insteadof A;
        A</span>::<span>bigTalk insteadof B;
    }
}

</span><span>class</span><span> Aliased_Talker {
    </span><span>use</span> A,<span> B {
        B</span>::<span>smallTalk insteadof A;
        A</span>::<span>bigTalk insteadof B;
        B</span>::bigTalk <span>as</span><span> talk;
    }
}
</span>?>
Copy after login

在本例中 Talker 使用了 trait A 和 B。由于 A 和 B 有冲突的方法，其定义了使用 trait B 中的 smallTalk 以及 trait A 中的 bigTalk。

Aliased_Talker 使用了 as 操作符来定义了 talk 来作为 B 的 bigTalk 的别名。

修改方法的访问控制

使用 as 语法还可以用来调整方法的访问控制。

修改方法的访问控制的例子

<?<span>php
trait HelloWorld {
    </span><span>public</span> <span>function</span><span> sayHello() {
        </span><span>echo</span> 'Hello World!'<span>;
    }
}

</span><span>//</span><span> 修改 sayHello 的访问控制</span>
<span>class</span><span> MyClass1 {
    </span><span>use</span> HelloWorld { sayHello <span>as</span> <span>protected</span><span>; }
}

</span><span>//</span><span> 给方法一个改变了访问控制的别名
// 原版 sayHello 的访问控制则没有发生变化</span>
<span>class</span><span> MyClass2 {
    </span><span>use</span> HelloWorld { sayHello <span>as</span> <span>private</span><span> myPrivateHello; }
}
</span>?>
Copy after login

从 trait 来组成 trait

正如类能够使用 trait 一样，其它 trait 也能够使用 trait。在 trait 定义时通过使用一个或多个 trait，它能够组合其它 trait 中的部分或全部成员。

从 trait 来组成 trait的例子

<?<span>php
trait Hello {
    </span><span>public</span> <span>function</span><span> sayHello() {
        </span><span>echo</span> 'Hello '<span>;
    }
}

trait World {
    </span><span>public</span> <span>function</span><span> sayWorld() {
        </span><span>echo</span> 'World!'<span>;
    }
}

trait HelloWorld {
    </span><span>use</span> Hello,<span> World;
}

</span><span>class</span><span> MyHelloWorld {
    </span><span>use</span><span> HelloWorld;
}

</span><span>$o</span> = <span>new</span><span> MyHelloWorld();
</span><span>$o</span>-><span>sayHello();
</span><span>$o</span>-><span>sayWorld();
</span>?>
Copy after login

以上例程会输出：Hello World!

Trait 的抽象成员

为了对使用的类施加强制要求，trait 支持抽象方法的使用。

表示通过抽象方法来进行强制要求的例子

<?<span>php
trait Hello {
    </span><span>public</span> <span>function</span><span> sayHelloWorld() {
        </span><span>echo</span> 'Hello'.<span>$this</span>-><span>getWorld();
    }
    </span><span>abstract</span> <span>public</span> <span>function</span><span> getWorld();
}

</span><span>class</span><span> MyHelloWorld {
    </span><span>private</span> <span>$world</span><span>;
    </span><span>use</span><span> Hello;
    </span><span>public</span> <span>function</span><span> getWorld() {
        </span><span>return</span> <span>$this</span>-><span>world;
    }
    </span><span>public</span> <span>function</span> setWorld(<span>$val</span><span>) {
        </span><span>$this</span>->world = <span>$val</span><span>;
    }
}
</span>?>
Copy after login

Trait 的静态成员

Traits 可以被静态成员静态方法定义。

静态变量的例子

<?<span>php
trait Counter {
    </span><span>public</span> <span>function</span><span> inc() {
        </span><span>static</span> <span>$c</span> = 0<span>;
        </span><span>$c</span> = <span>$c</span> + 1<span>;
        </span><span>echo</span> "<span>$c</span>\n"<span>;
    }
}

</span><span>class</span><span> C1 {
    </span><span>use</span><span> Counter;
}

</span><span>class</span><span> C2 {
    </span><span>use</span><span> Counter;
}

</span><span>$o</span> = <span>new</span> C1(); <span>$o</span>->inc(); <span>//</span><span> echo 1</span>
<span>$p</span> = <span>new</span> C2(); <span>$p</span>->inc(); <span>//</span><span> echo 1</span>
?>
Copy after login

静态方法的例子

<?<span>php
trait StaticExample {
    </span><span>public</span> <span>static</span> <span>function</span><span> doSomething() {
        </span><span>return</span> 'Doing something'<span>;
    }
}

</span><span>class</span><span> Example {
    </span><span>use</span><span> StaticExample;
}

Example</span>::<span>doSomething();
</span>?>
Copy after login

静态变量和静态方法的例子

<?<span>php
trait Counter {
    </span><span>public</span> <span>static</span> <span>$c</span> = 0<span>;
    </span><span>public</span> <span>static</span> <span>function</span><span> inc() {
        self</span>::<span>$c</span> = self::<span>$c</span> + 1<span>;
        </span><span>echo</span> self::<span>$c</span> . "\n"<span>;
    }
}

</span><span>class</span><span> C1 {
    </span><span>use</span><span> Counter;
}

</span><span>class</span><span> C2 {
    </span><span>use</span><span> Counter;
}

C1</span>::inc(); <span>//</span><span> echo 1</span>
C2::inc(); <span>//</span><span> echo 1</span>
?>
Copy after login

属性

Trait 同样可以定义属性。

定义属性的例子

<?<span>php
trait PropertiesTrait {
    </span><span>public</span> <span>$x</span> = 1<span>;
}

</span><span>class</span><span> PropertiesExample {
    </span><span>use</span><span> PropertiesTrait;
}

</span><span>$example</span> = <span>new</span><span> PropertiesExample;
</span><span>$example</span>-><span>x;
</span>?>
Copy after login

如果 trait 定义了一个属性，那类将不能定义同样名称的属性，否则会产生一个错误。如果该属性在类中的定义与在 trait 中的定义兼容（同样的可见性和初始值）则错误的级别是 E_STRICT，否则是一个致命错误。

冲突的例子

<?<span>php
trait PropertiesTrait {
    </span><span>public</span> <span>$same</span> = <span>true</span><span>;
    </span><span>public</span> <span>$different</span> = <span>false</span><span>;
}

</span><span>class</span><span> PropertiesExample {
    </span><span>use</span><span> PropertiesTrait;
    </span><span>public</span> <span>$same</span> = <span>true</span>; <span>//</span><span> Strict Standards</span>
    <span>public</span> <span>$different</span> = <span>true</span>; <span>//</span><span> 致命错误</span>
<span>}
</span>?>
Copy after login

Use的不同

不同use的例子

<?<span>php
namespace Foo\Bar;
</span><span>use</span> Foo\Test;  <span>//</span><span> means \Foo\Test - the initial \ is optional</span>
?>

<?<span>php
namespace Foo\Bar;
</span><span>class</span><span> SomeClass {
    </span><span>use</span> Foo\Test;   <span>//</span><span> means \Foo\Bar\Foo\Test</span>
<span>}
</span>?>
Copy after login

第一个use是用于 namespace 的 use Foo\Test，找到的是 \Foo\Test，第二个 use 是使用一个trait，找到的是\Foo\Bar\Foo\Test。

__CLASS__和__TRAIT__

__CLASS__ 返回 use trait 的 class name，__TRAIT__返回 trait name

示例如下

<?<span>php
trait TestTrait {
    </span><span>public</span> <span>function</span><span> testMethod() {
        </span><span>echo</span> "Class: " . <span>__CLASS__</span> . <span>PHP_EOL</span><span>;
        </span><span>echo</span> "Trait: " . __TRAIT__ . <span>PHP_EOL</span><span>;
    }
}

</span><span>class</span><span> BaseClass {
    </span><span>use</span><span> TestTrait;
}

</span><span>class</span> TestClass <span>extends</span><span> BaseClass {

}

</span><span>$t</span> = <span>new</span><span> TestClass();
</span><span>$t</span>-><span>testMethod();

</span><span>//</span><span>Class: BaseClass
//Trait: TestTrait</span>
Copy after login

Trait单例

实例如下

<?<span>php

trait singleton {    
    </span><span>/*</span><span>*
     * private construct, generally defined by using class
     </span><span>*/</span>
    <span>//</span><span>private function __construct() {}</span>
    
    <span>public</span> <span>static</span> <span>function</span><span> getInstance() {
        </span><span>static</span> <span>$_instance</span> = <span>NULL</span><span>;
        </span><span>$class</span> = <span>__CLASS__</span><span>;
        </span><span>return</span> <span>$_instance</span> ?: <span>$_instance</span> = <span>new</span> <span>$class</span><span>;
    }
    
    </span><span>public</span> <span>function</span><span> __clone() {
        </span><span>trigger_error</span>('Cloning '.<span>__CLASS__</span>.' is not allowed.',<span>E_USER_ERROR</span><span>);
    }
    
    </span><span>public</span> <span>function</span><span> __wakeup() {
        </span><span>trigger_error</span>('Unserializing '.<span>__CLASS__</span>.' is not allowed.',<span>E_USER_ERROR</span><span>);
    }
}

</span><span>/*</span><span>*
* Example Usage
</span><span>*/</span>

<span>class</span><span> foo {
    </span><span>use</span><span> singleton;
    
    </span><span>private</span> <span>function</span><span> __construct() {
        </span><span>$this</span>->name = 'foo'<span>;
    }
}

</span><span>class</span><span> bar {
    </span><span>use</span><span> singleton;
    
    </span><span>private</span> <span>function</span><span> __construct() {
        </span><span>$this</span>->name = 'bar'<span>;
    }
}

</span><span>$foo</span> = foo::<span>getInstance();
</span><span>echo</span> <span>$foo</span>-><span>name;

</span><span>$bar</span> = bar::<span>getInstance();
</span><span>echo</span> <span>$bar</span>->name;
Copy after login

调用trait方法

虽然不很明显，但是如果Trait的方法可以被定义为在普通类的静态方法，就可以被调用

实例如下

<?<span>php 
trait Foo { 
    </span><span>function</span><span> bar() { 
        </span><span>return</span> 'baz'<span>; 
    } 
} 

</span><span>echo</span> Foo::bar(),"\\n"<span>; 
</span>?>
Copy after login

 

www.bkjia.comtruehttp: //www.bkjia.com/PHPjc/927470.htmlTechArticlePHP learning--Traits new features, php--traits new features I came into contact with traits when reading the yii2 source code , I just studied it and wrote a blog to record it. As of PHP 5.4.0, PHP implements...
Related labels：
php
source：php.cn
Previous article：PHP prompts Warning: mysql_fetch_array() expects solution, expects_PHP tutorial Next article：PHP realizes the method of converting scientific notation into original number string, counting string_PHP tutorial
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Latest Articles by Author
Latest Issues
PHP arrays obtained from URL parameters do not behave as expected I have a URL parameter that contains the category ID and I want to treat it as an array li...
From 2024-04-06 22:09:02
0
1
1428
Where should I place CustomLog directive in apache I'm using php:7.2-apachedocker. I need to disable health check url login access log. Based...
From 2024-04-06 22:03:59
0
1
990
What is the format of the variables in the return value? I am a new learner of php. I found a piece of code: if($x<time()){return[false,'error']...
From 2024-04-06 21:55:20
0
1
778
Problems encountered when using opentbs to generate odt files: values ​​of the same key are displayed in the same row instead of separate columns. I'm using a library called OpenTbs to create odt using PHP, I'm using it because columns a...
From 2024-04-06 20:18:18
0
1
483
Group MySQL results by ID for looping over I have a table with flight data in mysql. I'm writing a php code that will group and displ...
From 2024-04-06 17:27:56
0
1
406
Related Topics
More>
Popular Recommendations
Popular Tutorials
More>
Related Tutorials
Popular Recommendations
Latest courses
Latest Downloads
More>
Web Effects
Website Source Code
Website Materials
Front End Template