How to use traits in php

Since PHP 5.4.0, PHP implements a method of code reuse called traits.

Trait is a code reuse mechanism prepared for single inheritance languages ​​like PHP. Traits are designed to reduce the limitations of single-inheritance languages ​​and allow developers to freely reuse methods in independent classes within different hierarchies. The semantics of Trait and Class composition define a way to reduce complexity and avoid the typical problems associated with traditional multiple inheritance and Mixin classes.

Trait is similar to Class, but is only designed to combine functionality in a fine-grained and consistent way. Cannot be instantiated through the trait itself. It adds a combination of horizontal features to traditional inheritance; that is, there is no need for inheritance between several Classes in an application.

This article mainly introduces how to use traits in PHP. To put it simply, the trait keyword is used in PHP to solve the problem that a class wants to integrate the attributes and properties of the base class. Method , but also want to have other base class methods, and trait is generally used in conjunction with use.

<?php
  trait Drive {
    public $carName = &#39;trait&#39;;
    public function driving() {
      echo "driving {$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();

?>

The output results are as follows:

study
eat
driving trait

In the above example, the Student class inherits Person and has the eat method, and by combining Drive, it has the driving method and attribute carName.

If there is a property or method with the same name in Trait, base class and this class, which one will be retained in the end?

<?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();
?>

The output results are as follows:

hello student
driving from drive

So we can conclude that when a method or attribute has the same name, the method in the current class will override the trait's method, and the trait's method will override the base class. method in.

If you want to combine multiple Traits, separate the Trait names by commas:

use Trait1, Trait2;

What happens if multiple Traits contain methods or properties with the same name? The answer is that when multiple combined Traits contain properties or methods with the same name, they need to be explicitly declared to resolve conflicts, otherwise a fatal error will occur.

<?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;
}
?>

The output results are as follows:

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

Use insteadof and asoperators to resolve conflicts. Insteadof uses a method to replace another, and as is used to replace the method. An alias, please see the code for specific usage:

<?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();
?>

The output result is as follows:

Trait2::hello
Trait1::hi

Trait2::hello
Trait1::hi
Trait2::hi
Trait1::hello

The as keyword has another use, which is to modify the access control of the method:

Trait can also be combined with Trait. Trait supports abstract methods, static properties and static methods. The test code is as follows:

<?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 &#39;get World&#39;;
  }
}
$Obj = new HelloWorld();
$Obj->sayHello();
$Obj->sayWorld();
echo $Obj->getWorld() . "\n";
HelloWorld::doSomething();
$Obj->inc();
$Obj->inc();
?>

The output result is as follows:

Hello
World
get World
Doing something
1
2

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