Detailed explanation of static members, abstract members, and attribute codes of php traits

Abstract members of Trait

In order to enforce requirements on the classes used, traits support the use of abstract methods.

Indicates an example of mandatory requirements through abstract methods

<?php
trait Hello {
    public function sayHelloWorld() {
        echo &#39;Hello&#39;.$this->getWorld();
    }
    abstract public function getWorld();
}
class MyHelloWorld {
    private $world;
    use Hello;
    public function getWorld() {
        return $this->world;
    }
    public function setWorld($val) {
        $this->world = $val;
    }
}
?>

Trait's static members

Traits can be static members Static method definition.

staticExamples of variables

<?php
trait Counter {
    public function inc() {
        static $c = 0;
        $c = $c + 1;
        echo "$c\n";
    }
}
class C1 {
    use Counter;
}
class C2 {
    use Counter;
}
$o = new C1(); $o->inc(); // echo 1
$p = new C2(); $p->inc(); // echo 1
?>

Examples of static methods

<?php
trait StaticExample {
    public static function doSomething() {
        return &#39;Doing something&#39;;
    }
}
class Example {
    use StaticExample;
}
Example::doSomething();
?>

Examples of static variables and static methods

<?php
trait Counter {
    public static $c = 0;
    public static function inc() {
        self::$c = self::$c + 1;
        echo self::$c . "\n";
    }
}
class C1 {
    use Counter;
}
class C2 {
    use Counter;
}
C1::inc(); // echo 1
C2::inc(); // echo 1
?>

Attribute

Trait can also define attributes.

Example of defining attributes

<?php
trait PropertiesTrait {
    public $x = 1;
}

class PropertiesExample {
    use PropertiesTrait;
}

$example = new PropertiesExample;
$example->x;
?>

If a trait defines an attribute, the class will not be able to define an attribute with the same name, otherwise an error will be generated. If the property's definition in the class is compatible with its definition in the trait (same visibility and initial value) the error level is E_STRICT, otherwise it is a fatal error.

Conflict examples

<?php
trait PropertiesTrait {
    public $same = true;
    public $different = false;
}

class PropertiesExample {
    use PropertiesTrait;
    public $same = true; // Strict Standards
    public $different = true; // 致命错误
}
?>

Differences in Use

Examples of different uses

<?php
namespace Foo\Bar;
use Foo\Test;  // means \Foo\Test - the initial \ is optional
?>
<?php
namespace Foo\Bar;
class SomeClass {
    use Foo\Test;   // means \Foo\Bar\Foo\Test
}
?>

The first use is use Foo\Test for namespace, What was found was \Foo\Test. The second use was to use a trait and what was found was \Foo\Bar\Foo\Test.

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