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PHP是單繼承的語言,在PHP 5.4 Traits出現(xiàn)之前,PHP的類無法同時(shí)從兩個(gè)基類繼承屬性或辦法.php的Traits和Go語言的組合功能類似,通過在類中使用use關(guān)鍵字聲明要組合的Trait名稱,而具體某個(gè)Trait的聲明使用trait關(guān)鍵詞,Trait不能直接實(shí)例化.具體用法請(qǐng)看下面的代碼:PHP應(yīng)用
<?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:PHP應(yīng)用
study eat driving trait
上面的例子中,Student類通過繼承Person,有了eat辦法,通過組合Drive,有了driving辦法和屬性carName.PHP應(yīng)用
如果Trait、基類和本類中都存在某個(gè)同名的屬性或者辦法,最終會(huì)保留哪一個(gè)呢?通過下面的代碼測(cè)試一下:PHP應(yīng)用
<?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:PHP應(yīng)用
hello student driving from drive
因此得出結(jié)論:當(dāng)辦法或?qū)傩酝麜r(shí),當(dāng)前類中的辦法會(huì)覆蓋 trait的 辦法,而 trait 的辦法又覆蓋了基類中的辦法.PHP應(yīng)用
如果要組合多個(gè)Trait,通過逗號(hào)分隔 Trait名稱:PHP應(yīng)用
use Trait1, Trait2;
PHP應(yīng)用
如果多個(gè)Trait中包含同名辦法或者屬性時(shí),會(huì)怎樣呢?答案是當(dāng)組合的多個(gè)Trait包含同名屬性或者辦法時(shí),需要明確聲明解決沖突,否則會(huì)產(chǎn)生一個(gè)致命錯(cuò)誤.PHP應(yīng)用
<?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:PHP應(yīng)用
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(gè)辦法替代另一個(gè),而as是給辦法取一個(gè)別名,具體用法請(qǐng)看代碼:PHP應(yīng)用
<?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:PHP應(yīng)用
Trait2::hello Trait1::hi Trait2::hello Trait1::hi Trait2::hi Trait1::hello
as關(guān)鍵詞還有另外一個(gè)用途,那就是修改方法的拜訪控制:PHP應(yīng)用
<?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(); # 報(bào)致命錯(cuò)誤,因?yàn)閔ello辦法被修改成受保護(hù)的 $Obj2 = new Class2(); $Obj2->hello(); # 原來的hello辦法仍然是公共的 $Obj2->hi(); # 報(bào)致命錯(cuò)誤,因?yàn)閯e名hi辦法被修改成私有的
Trait 也能組合Trait,Trait中支持抽象辦法、靜態(tài)屬性及靜態(tài)辦法,測(cè)試代碼如下:PHP應(yīng)用
<?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:PHP應(yīng)用
Hello World get World Doing something 1 2
以上就是本文的全部內(nèi)容,希望對(duì)大家的學(xué)習(xí)有所贊助.PHP應(yīng)用
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