說通俗點,在PHP中使用trait關鍵字是為了解決一個類別既想整合基類的屬性和方法,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。
下面就來看一下本篇文章介紹的PHP中trait使用方法
<?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(); ?>
輸出結果如下:
study eat driving trait
上面的範例中,Student類別透過繼承Person,有了eat方法,透過組合Drive,有了driving方法和屬性carName。
如果Trait、基底類別和本類別中都存在某個同名的屬性或是方法,最後會保留哪一個呢?
<?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(); ?>
輸出結果如下:
hello student driving from drive
因此得出結論:當方法或屬性同名時,目前類別中的方法會覆寫trait的方法,而trait 的方法又覆寫了基底類別中的方法。
如果要組合多個Trait,透過逗號分隔 Trait名稱:
use Trait1, Trait2;
如果多個Trait中包含同名方法或屬性時,會怎麼樣呢?答案是當組合的多個Trait包含同名屬性或方法時,需要明確聲明解決衝突,否則會產生一個致命錯誤。
<?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; } ?>
輸出結果如下:
程式碼如下:
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操作子來解決衝突,insteadof是用某個方法替代另一個,而as是給方法取一個別名,具體用法請看程式碼:
<?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(); ?>
輸出結果如下:
Trait2::hello Trait1::hi Trait2::hello Trait1::hi Trait2::hi Trait1::hello
as關鍵字還有另一個用途,那就是修改方法的存取控制:
Trait 也能組合Trait,Trait中支援抽象方法、靜態屬性及靜態方法,測試程式碼如下:
<?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(); ?>
輸出結果如下:
Hello World get World Doing something 1 2
以上是最新的PHP trait使用方法詳解的詳細內容。更多資訊請關注PHP中文網其他相關文章!