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老师批语：trait , 更准确的说法, 是从个方法集中获取内容, 相当于当前类的功能扩展, 与传统意义上的继承, 还是有很大区别的
一，Trart用途：可以使子类无法从多个类中继承属性和方法
class animal{
public function a(){
echo 'this is animal.';
}
}
trait cat{
public function b(){
echo 'this is cat.';
}
}
trait pig{
public function c(){
echo 'this is pig;';
}
}
class dog extends animal{
use cat;
use pig;
public function get(){
echo 'this is big dog.';
}
}
$dog=new dog();
$dog->a();//返回this is animal.
echo '<br>';
$dog->b();//返回this is cat.
echo '<br>';
$dog->c();//返回this is pig;点击 "运行实例" 按钮查看在线实例
二，当子类中有和trait中重名的属性和方法时，trait中的属性和方法会被覆盖
实例
trait pig{
public function c(){
echo 'this is pig;';
}
}
class dog extends animal{
use cat;
use pig;
public function c(){
echo 'this is big dog.';
}
}
$dog=new dog();
$dog->a();//返回this is animal.
echo '<br>';
$dog->b();//返回this is cat.
echo '<br>';
$dog->c();//返回this is big pig;点击 "运行实例" 按钮查看在线实例
trait pig{
public function c(){
echo 'this is pig;';
}
}
class dog extends animal{
use cat;
use pig;
public function c(){
echo 'this is big dog.';
}
}
$dog=new dog();
$dog->a();//返回this is animal.
echo '<br>';
$dog->b();//返回this is cat.
echo '<br>';
$dog->c();//返回this is big pig;点击 "运行实例" 按钮查看在线实例
三，当trait和父类中有同名的属性和方法时，父类中的属性和方法将会被 trait中的属性和方法覆盖
class animal{
public function a(){
echo 'this is animal.';
}
}
trait cat{
public function a(){
echo 'this is cat.';
}
}
class dog extends animal{
use cat;
public function c(){
echo 'this is big dog.';
}
}
$dog=new dog();
$dog->a();//返回this is cat.点击 "运行实例" 按钮查看在线实例
总结：trait可以实现一个子类引用其父类之外的属性和方法，当有同名的属性和方法时，优先级为：子类>trait>父类
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