How to use traits to achieve PHP code reuse

This article mainly introduces the examples of using traits to implement code reuse in PHP. This article explains the simple use of Traits, priority issues, multiple Trait conflict issues, and how as can be used to modifyAccess Control, the use of Trait in Trait, etc. Friends who need it can refer to

Traits were added after PHP5.4 to implement the code reuse mechanism. Traits are similar to classes, but cannot be instantiated. There is no need to inherit, just use the keyword use to introduce it in the class. Multiple Traits can be introduced, separated by ','.

(1) Trait is simple to use

var1; //test1
$c->test2(); //trait B::test2()

(2) Priority issue
Trait will override the inherited method, and the current class will Override Trait methods.

trait A {
  public $var1 = 'test';
  public function test() {
    echo 'A::test()';
  }
  public function test1() {
    echo 'A::test1()';
  }
}
 
class B {
  public function test() {
    echo 'B::test()';
  }
  public function test1() {
    echo 'B::test1()';
  }
}
class C extends B{
  use A;
  public function test() {
    echo 'c::test()';
  }
}
 
$c = new C();
$c->test(); //c::test()
$c->test1(); //A::test1()

(3) Multiple Trait conflict issues
If the conflict is not resolved, a fatal error will occur;
Insteadof can be used to clarify which method in the conflict to use;
You can use the as operator to rename one of the conflicting methods;

trait A {
  public function test() {
    echo 'A::test()';
  }
}
 
trait B {
  public function test() {
    echo 'B::test()';
  }
}
 
class C {
  use A,B {
    B::test insteadof A;
    B::test as t;
  }
}
 
$c = new C();
$c->test(); //B::test()
$c->t(); //B::test()  可以用as另起名

(4) as can be used to modify method access control

trait HelloWorld {
  public function sayHello () {
    echo 'Hello World!' ;
  }
}
 
// 修改 sayHello 的访问控制
class A {
  use HelloWorld { sayHello as protected; }
}
 
// 给方法一个改变了访问控制的别名
// 原版 sayHello 的访问控制则没有发生变化
class B {
  use HelloWorld { sayHello as private myPrivateHello ; }
}
 
$b = new A();
$b->sayHello(); //Fatal error: Call to protected method A::sayHello() from context ''

(5) Trait is used in Trait

trait A {
  public function test1() {
    echo 'test1';
  }
}
 
trait B {
  public function test2() {
    echo 'test2';
  }
}
 
trait C {
  use A,B;
}
 
class D {
  use C;
}
 
$d = new D();
$d->test2(); //test2

(6) Trait supports abstract methods, supports static methods, and cannot directly define static variables, but static variables Can be referenced by trait method .

trait A {
  public function test1() {
    static $a = 0;
    $a++;
    echo $a;
  }
 
  abstract public function test2(); //可定义抽象方法
}
 
class B {
  use A;
  public function test2() {
 
  }
}
 
$b = new B();
$b->test1(); //1
$b->test1(); //2

(7) Trait can define attributes, but the same name attribute cannot be defined in the class

trait A {
  public $test1;
}
 
class B {
  use A;
  public $test2;
}

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