A simple tutorial on reusing PHP code

Since PHP 5.4.0, PHP implements a code reuse method called Trait.

Traits is a code reuse mechanism prepared for single inheritance languages ​​like PHP. Trait To reduce the limitations of single-inheritance languages ​​and give developers the freedom to reuse method sets in independent classes within different hierarchies. Traits The semantics of class composition define a way to reduce complexity and avoid the typical problems associated with traditional multiple inheritance and mixins.

Simple use

<?phptrait Test
{    public function echoHello()
    {        echo &#39;Hello Trait&#39;;
    }
}class Base{    public function index()
    {        echo &#39;index&#39;;
    }
}class One extends Base{    use Test;
}class Two extends Base{    use Test;
}
$one = new One();
$two = new Two();echo $one->echoHello();echo $one->index();echo $two->echoHello();

The result output is Hello Trait index Hello Trait.

Members inherited from the base class will be overwritten by members inserted by Trait. The order of precedence is that members from the current class override Trait methods, and Traits override inherited methods.

<?php
trait Test{    public function echoHello()   
 {        echo &#39;Hello Trait&#39;;    }}class Base
 {    use Test;    public function echoHello()  
  {        echo &#39;Hello Base&#39;;    }}class One extends Base
  {    use Test;    public function echoHello()    
  {        echo &#39;Hello One&#39;;    }}class Two extends Base
  {    use Test;}$one = new One();$two = new Two();$base = new Base();
  echo $one->echoHello();echo $two->echoHello();echo $base->echoHello();
结果输出 Hello One Hello Trait Hello Base。
?>

class one example covers the base class and Trait Test, indicating that the method priority of the current class is higher than them.

class Two example covers the base class, Trait has priority higher than the inherited base class.

class Base example covers Trait Test, indicating that the method priority of the current class is higher than Trait.

Separate by commas, list multiple traits in the use statement, and they can all be inserted into a class.

<?phptrait Test
{    public function echoHello()
    {        echo &#39;Hello &#39;;
    }
}trait TestTwo
{    public function echoWord()
    {        echo &#39;word !&#39;;
    }
}class One{    use Test,TestTwo;
}
$one  = new One();echo $one->echoHello();echo $one->echoWord();

The result output is Hello word!.

If two Traits insert a method with the same name, a fatal error will occur if the conflict is not explicitly resolved.

<?phptrait Test
{    public function echoHello()
    {        echo &#39;Hello Test&#39;;
    }    public function echoWord()
    {        echo &#39;word Test&#39;;
    }
}trait TestTwo
{    public function echoHello()
    {        echo &#39;Hello TestTwo &#39;;
    }    public function echoWord()
    {        echo &#39;word TestTwo&#39;;
    }
}class One{    use Test, TestTwo {        Test::echoHello as echoTest;
        Test::echoWord insteadof TestTwo;
        TestTwo::echoHello insteadof Test;
    }
}
$one = new One();echo $one->echoTest();echo $one->echoWord();echo $one->echoHello();

Output result: Hello Test word Test Hello TestTwo.

Use as as an alias, that is, Test::echoHello as echoTest; output echoHello in Trait Test.

Use insteadof operator to exclude other Traits, that is, Test::echoWord instead of TestTwo ; The output is word Test, use echoWord

Modify the control permissions of the method in Trait Test

<?phptrait Test
{    public function echoHello()
    {        echo &#39;Hello&#39;;
    }    public function echoWord()
    {        echo &#39;word&#39;;
    }
}trait TestTwo
{    public function echoHello()
    {        echo &#39;Hello TestTwo &#39;;
    }    public function echoWord()
    {        echo &#39;word TestTwo&#39;;
    }
}class One{    use Test {        echoHello as private;
    }
}class Two{    use Test {        echoHello as private echoTwo;
    }
}
$one = new One();
$two = new Two();echo $two->echoHello();

to output the result Hello.

Use as in class one to make echoHello private, then echoHello cannot be accessed through class one.

Use as in class two to rename it first, and then set the new naming method as private. The methods in the original Trait can be accessed normally.

Trait can also define properties like a class. It’s very useful!

The above are some basic uses of Traits. For more details, please refer to the official manual. Here are a few things to note: Point: Trait will override the parent class method inherited by the calling class. Trait cannot be instantiated using new like Class.

A single Trait can be composed of multiple Traits. In a single Class, multiple Traits can be used. Trait supports modification. Words (modifiers), such as final, static, abstract, we can use insteadof and as operators to resolve conflicts between Traits.

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