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PHP中trait使用方法

來源:技術(shù)員聯(lián)盟┆發(fā)布時間:2017-10-15 06:41┆點擊:

說通俗點,PHP中使用trait關(guān)鍵字是為了解決一個類既想集成基類的屬性和方法,又想擁有別的基類的方法,而trait一般情況下是和use搭配使用的。

<?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(); ?>

輸出結(jié)果如下:

study eat driving trait

上面的例子中,Student類通過繼承Person,有了eat方法,通過組合Drive,有了driving方法和屬性carName。

如果Trait、基類和本類中都存在某個同名的屬性或者方法,最終會保留哪一個呢?

<?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(); ?>

輸出結(jié)果如下:

hello student driving from drive

因此得出結(jié)論:當(dāng)方法或?qū)傩酝麜r,當(dāng)前類中的方法會覆蓋 trait的 方法,而 trait 的方法又覆蓋了基類中的方法。

如果要組合多個Trait,通過逗號分隔 Trait名稱:

use Trait1, Trait2;

如果多個Trait中包含同名方法或者屬性時,會怎樣呢?答案是當(dāng)組合的多個Trait包含同名屬性或者方法時,需要明確聲明解決沖突,否則會產(chǎn)生一個致命錯誤。

<?php trait 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; } ?>

輸出結(jié)果如下:

復(fù)制代碼 代碼如下:


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操作符來解決沖突,insteadof是使用某個方法替代另一個,而as是給方法取一個別名,具體用法請看代碼:

<?php trait 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(); ?>

輸出結(jié)果如下:

Trait2::hello Trait1::hi Trait2::hello Trait1::hi Trait2::hi Trait1::hello

as關(guān)鍵詞還有另外一個用途,那就是修改方法的訪問控制:

Trait 也能組合Trait,Trait中支持抽象方法、靜態(tài)屬性及靜態(tài)方法,測試代碼如下:

<?php trait 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(); ?>

輸出結(jié)果如下:

Hello World get World Doing something 1 2