【转】PHP的Trait 特性，phptrait特性

【转】PHP的Trait 特性，phptrait特性

Trait是在PHP5.4中加入的，它既不是接口也不是类。主要是为了解决单继承语言的限制。是PHP多重继承的一种解决方案。例如，需要同时继承两个 Abstract Class， 这将会是件很麻烦的事情，Trait 就是为了解决这个问题。它能被加入到一个或多个已经存在的类中。它声明了类能做什么（表明了其接口特性），同时也包含了具体实现（表明了其类特性）

简单使用

首先，当然是声明个 Trait，PHP5.4 增加了 trait 关键字

<span>1</span> <span>trait first_trait {
</span><span>2</span>      <span>function</span> first_method() { <span>/*</span><span> Code Here </span><span>*/</span><span> }
</span><span>3</span>      <span>function</span> second_method() { <span>/*</span><span> Code Here </span><span>*/</span><span> }
</span><span>4</span> }

同时，如果要在 Class 中使用该 Trait，那么使用 use 关键字

<span> 1</span> <span>class</span><span> first_class {
</span><span> 2</span>     <span>//</span><span> 注意这行，声明使用 first_trait</span>
<span> 3</span>     <span>use</span><span> first_trait;
</span><span> 4</span> <span>}
</span><span> 5</span> 
<span> 6</span> <span>$obj</span> = <span>new</span><span> first_class();
</span><span> 7</span> 
<span> 8</span> <span>//</span><span> Executing the method from trait</span>
<span> 9</span> <span>$obj</span>->first_method(); <span>//</span><span> valid</span>
<span>10</span> <span>$obj</span>->second_method(); <span>//</span><span> valid</span>

使用多个 Trait

在同个 Class 中可以使用多个 Trait

<span> 1</span> <span>trait first_trait
</span><span> 2</span> <span>{
</span><span> 3</span>     <span>function</span> first_method() { <span>echo</span> "method1"<span>; }
</span><span> 4</span> <span>}
</span><span> 5</span> 
<span> 6</span> <span>trait second_trait {
</span><span> 7</span>     <span>function</span> second_method() { <span>echo</span> "method2"<span>; }
</span><span> 8</span> <span>}
</span><span> 9</span> 
<span>10</span> <span>class</span><span> first_class {
</span><span>11</span>     <span>//</span><span> now using more than one trait</span>
<span>12</span>     <span>use</span> first_trait,<span> second_trait;
</span><span>13</span> <span>}
</span><span>14</span> 
<span>15</span> <span>$obj</span>= <span>new</span><span> first_class();
</span><span>16</span> 
<span>17</span> <span>//</span><span> Valid</span>
<span>18</span> <span>$obj</span>->first_method(); <span>//</span><span> Print : method1
</span><span>19</span> 
<span>20</span> <span>// Valid</span>
<span>21</span> <span>$obj</span>->second_method(); <span>//</span><span> Print : method2</span>

Trait 之间的嵌套

同时，Trait 之间也可以相互的嵌套，例如

<span> 1</span> <span>trait first_trait {
</span><span> 2</span>     <span>function</span> first_method() { <span>echo</span> "method1"<span>; }
</span><span> 3</span> <span>}
</span><span> 4</span> 
<span> 5</span> <span>trait second_trait {
</span><span> 6</span>     <span>use</span><span> first_trait;
</span><span> 7</span>     <span>function</span> second_method() { <span>echo</span> "method2"<span>; }
</span><span> 8</span> <span>}
</span><span> 9</span> 
<span>10</span> <span>class</span><span> first_class {
</span><span>11</span>     <span>//</span><span> now using </span>
<span>12</span>     <span>use</span><span> second_trait;
</span><span>13</span> <span>}
</span><span>14</span> 
<span>15</span> <span>$obj</span>= <span>new</span><span> first_class();
</span><span>16</span> 
<span>17</span> <span>//</span><span> Valid</span>
<span>18</span> <span>$obj</span>->first_method(); <span>//</span><span> Print : method1
</span><span>19</span> 
<span>20</span> <span>// Valid</span>
<span>21</span> <span>$obj</span>->second_method(); <span>//</span><span> Print : method2</span>

Trait 的抽象方法（Abstract Method）

我们可以在 Trait 中声明需要实现的抽象方法，这样能使使用它的 Class 必须实现它

<span> 1</span> <span>trait first_trait {
</span><span> 2</span>     <span>function</span> first_method() { <span>echo</span> "method1"<span>; }
</span><span> 3</span> 
<span> 4</span>     <span>//</span><span> 这里可以加入修饰符，说明调用类必须实现它</span>
<span> 5</span>     <span>abstract</span> <span>public</span> <span>function</span><span> second_method();
</span><span> 6</span> <span>}
</span><span> 7</span> 
<span> 8</span> <span>class</span><span> first_method {
</span><span> 9</span>     <span>use</span><span> first_trait;
</span><span>10</span> 
<span>11</span>     <span>function</span><span> second_method() {
</span><span>12</span>         <span>/*</span><span> Code Here </span><span>*/</span>
<span>13</span> <span>    }
</span><span>14</span> }

Trait 冲突

多个 Trait 之间同时使用难免会冲突，这需要我们去解决。PHP5.4 从语法方面带入了相关 的关键字语法：insteadof 以及 as ，用法参见

<span> 1</span> <span>trait first_trait {
</span><span> 2</span>     <span>function</span><span> first_function() { 
</span><span> 3</span>         <span>echo</span> "From First Trait"<span>;
</span><span> 4</span> <span>    }
</span><span> 5</span> <span>}
</span><span> 6</span> 
<span> 7</span> <span>trait second_trait {
</span><span> 8</span>     <span>//</span><span> 这里的名称和 first_trait 一样，会有冲突</span>
<span> 9</span>     <span>function</span><span> first_function() { 
</span><span>10</span>         <span>echo</span> "From Second Trait"<span>;
</span><span>11</span> <span>    }
</span><span>12</span> <span>}
</span><span>13</span> 
<span>14</span> <span>class</span><span> first_class {
</span><span>15</span>     <span>use</span> first_trait,<span> second_trait {
</span><span>16</span>         <span>//</span><span> 在这里声明使用 first_trait 的 first_function 替换
</span><span>17</span> <span>        // second_trait 中声明的</span>
<span>18</span>         first_trait::<span>first_function insteadof second_trait;
</span><span>19</span> <span>    }
</span><span>20</span> <span>}  
</span><span>21</span> 
<span>22</span> <span>$obj</span> = <span>new</span><span> first_class();
</span><span>23</span> 
<span>24</span> <span>//</span><span> Output: From First Trait</span>
<span>25</span> <span>$obj</span>->first_function();

上面就是些 Trait 比较基本的使用了，更详细的可以参考官方手册。这里总结下注意的几 点：

• Trait 会覆盖调用类继承的父类方法
• Trait 无法如 Class 一样使用 new 实例化
• 单个 Trait 可由多个 Trait 组成
• 在单个 Class 中，可以使用多个 Trait
• Trait 支持修饰词（modifiers），例如 final、static、abstract
• 我们能使用 insteadof 以及 as 操作符解决 Trait 之间的冲突

文章出处：http://www.kuqin.com/web/20111119/315048.html