PHP中使用trait關鍵字是為了解決一個類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。本文是本站小編搜尋整理的關於PHP中trait使用方法介紹,感興趣的朋友一起學習吧!!想了解更多相關資訊請持續關注我們應屆畢業生考試網!
<?php
trait Drive {
public $carName = 'trait';
public function driving() {
echo "driving {$this->carName}n";
}
}
class Person {
public function eat() {
echo "eatn";
}
}
class Student extends Person {
use Drive;
public function study() {
echo "studyn";
}
}
$student = new Student();
$student->study();
$student->eat();
$student->driving();
?>
輸出結果如下:
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 driven";
}
public function driving() {
echo "driving from driven";
}
}
class Person {
public function hello() {
echo "hello personn";
}
public function driving() {
echo "driving from personn";
}
}
class Student extends Person {
use Drive;
public function hello() {
echo "hello studentn";
}
}
$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,當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?答案是當組合的多個Trait包含同名屬性或者方法時,需要明確宣告解決衝突,否則會產生一個致命錯誤。
<?php
trait Trait1 {
public function hello() {
echo "Trait1::hellon";
}
public function hi() {
echo "Trait1::hin";
}
}
trait Trait2 {
public function hello() {
echo "Trait2::hellon";
}
public function hi() {
echo "Trait2::hin";
}
}
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_ on line 20
使用insteadof和as操作符來解決衝突,insteadof是使用某個方法替代另一個,而as是給方法取一個別名,具體用法請看程式碼:
<?php
trait Trait1 {
public function hello() {
echo "Trait1::hellon";
}
public function hi() {
echo "Trait1::hin";
}
}
trait Trait2 {
public function hello() {
echo "Trait2::hellon";
}
public function hi() {
echo "Trait2::hin";
}
}
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 "Hellon";
}
}
trait World {
use Hello;
public function sayWorld() {
echo "Worldn";
}
abstract public function getWorld();
public function inc() {
static $c = 0;
$c = $c + 1;
echo "$cn";
}
public static function doSomething() {
echo "Doing somethingn";
}
}
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