PHP7之Trait详解

用法：通过在类中使用use 关键字，声明要组合的Trait名称，具体的Trait的声明使用Trait关键词，Trait不能实例化

如下代码实例:

<?phptrait Dog{ ???public $name="dog"; ???public function bark(){ ???????echo "This is dog"; ???}}class Animal{ ???public function eat(){ ???????echo "This is animal eat"; ???}}class Cat extends Animal{ ???use Dog; ???public function drive(){ ???????echo "This is cat drive"; ???}}$cat = new Cat();$cat->drive();echo "<br/>";$cat->eat();echo "<br/>";$cat->bark();?>

将会如下输出

再测试Trait、基类和本类对同名属性或方法的处理，如下代码

<?phptrait Dog{ ???public $name="dog"; ???public function drive(){ ???????echo "This is dog drive"; ???} ???public function eat(){ ???????echo "This is dog eat"; ???}}class Animal{ ???public function drive(){ ???????echo "This is animal drive"; ???} ???public function eat(){ ???????echo "This is animal eat"; ???}}class Cat extends Animal{ ???use Dog; ???public function drive(){ ???????echo "This is cat drive"; ???}}$cat = new Cat();$cat->drive();echo "<br/>";$cat->eat();?>

如下显示

所以：Trait中的方法或属性会覆盖 基类中的同名的方法或属性，而本类会覆盖Trait中同名的属性或方法

一个类可以组合多个Trait，通过逗号相隔，如下

use trait1,trait2

当不同的trait中，却有着同名的方法或属性，会产生冲突，可以使用insteadof或 as进行解决，insteadof 是进行替代，而as是给它取别名
如下实例：

<?phptrait trait1{ ???public function eat(){ ???????echo "This is trait1 eat"; ???} ???public function drive(){ ???????echo "This is trait1 drive"; ???}}trait trait2{ ???public function eat(){ ???????echo "This is trait2 eat"; ???} ???public function drive(){ ???????echo "This is trait2 drive"; ???}}class cat{ ???use trait1,trait2{ ???????trait1::eat insteadof trait2; ???????trait1::drive insteadof trait2; ???}}class dog{ ???use trait1,trait2{ ???????trait1::eat insteadof trait2; ???????trait1::drive insteadof trait2; ???????trait2::eat as eaten; ???????trait2::drive as driven; ???}}$cat = new cat();$cat->eat();echo "<br/>";$cat->drive();echo "<br/>";echo "<br/>";echo "<br/>";$dog = new dog();$dog->eat();echo "<br/>";$dog->drive();echo "<br/>";$dog->eaten();echo "<br/>";$dog->driven();?>

输出如下

as 还可以修改方法的访问控制

<?phptrait Animal{ ???public function eat(){ ???????echo "This is Animal eat"; ???}}class Dog{ ???use Animal{ ???????eat as protected; ???}}class Cat{ ???use Animal{ ???????Animal::eat as private eaten; ???}}$dog = new Dog();$dog->eat();//报错，因为已经把eat改成了保护$cat = new Cat();$cat->eat();//正常运行，不会修改原先的访问控制$cat->eaten();//报错，已经改成了私有的访问控制?>

Trait也可以互相组合，还可以使用抽象方法，静态属性，静态方法等，实例如下

<?phptrait Cat{ ???public function eat(){ ???????echo "This is Cat eat"; ???}}trait Dog{ ???use Cat; ???public function drive(){ ???????echo "This is Dog drive"; ???} ???abstract public function getName(); ???????public function test(){ ???????static $num=0; ???????$num++; ???????echo $num; ???} ???????public static function say(){ ???????echo "This is Dog say"; ???}}class animal{ ???use Dog; ???public function getName(){ ???????echo "This is animal name"; ???}}$animal = new animal();$animal->getName();echo "<br/>";$animal->eat();echo "<br/>";$animal->drive();echo "<br/>";$animal::say();echo "<br/>";$animal->test();echo "<br/>";$animal->test();?>

输出如下