Detailed introduction to PHP type constraints (with code)

This article brings you a detailed introduction to PHP type constraints (with code). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Introduction: The so-called type constraint means that when defining a variable, its type must be specified, and the variable can only store data of this type in the future. Although PHP is a weakly typed language, it already supports type constraints in PHP 5, including objects, interfaces, and arrays. It supports scalar type constraints after PHP 7. Here are a few examples.

Scalar type, array

Specify the type in the parameter. If it is inconsistent, a catchable fatal error will be thrown

<?php /**
 * 数组类型约束
 * @param array $arr
 */
function printArray(array $arr)
{
    echo implode(&#39;,&#39;, $arr);
}

printArray(array(1, 2, 3));// 1,2,3
printArray(&#39;1&#39;);// Fatal error: Uncaught TypeError: Argument 1 passed to printArray() must be of the type array, string given, called in D:\WWW\test.php on line 13 and defined in D:\WWW\test.php:7 Stack trace: #0 D:\WWW\test.php(13): printArray(&#39;1&#39;) #1 {main} thrown in D:\WWW\test.php on line 7

As shown above , the same is true for scalar types

<?php /**
 * 标量类型约束
 * @param string $name
 * @param int $age
 * @param float $height
 * @param bool $isBoy
 */
function sayInfo(string $name, int $age, float $height, bool $isBoy)
{
    echo &#39;姓名：&#39; . $name . &#39;，年龄：&#39; . $age . &#39;，身高：&#39; . $height . &#39;，是否为男孩：&#39; . ($isBoy ? &#39;是&#39; : &#39;否&#39;);
}

sayInfo(&#39;tom&#39;, 12, 134.5, true);// 姓名：tom，年龄：12，身高：134.5，是否为男孩：是

Objects, interfaces

Type constraints can also be specified as objects or interfaces. First define a Human interface, and Boy and Girl two classes implement the interface respectively

<?php /**
 * 接口
 * Interface Human
 */
interface Human
{
    public function say();

    public function run();
}

/**
 * 实现 Human 接口
 * Class Boy
 */
class Boy implements Human
{
    public function say()
    {
        echo &#39;a boy say&#39;;
    }

    public function run()
    {
        echo &#39;a boy run&#39;;
    }
}

/**
 * 实现 Human 接口
 * Class Girl
 */
class Girl implements Human
{
    public function say()
    {
        echo &#39;a girl say&#39;;
    }

    public function run()
    {
        echo &#39;a girl run&#39;;
    }
}

Next, create a new class to test

<?php include &#39;./human.php&#39;;

class Action
{
    /**
     * Boy 对象类型约束
     * @param Boy $boy
     */
    public function boySay(Boy $boy)
    {
        $boy->say();
    }

    /**
     * Girl 对象类型约束
     * @param Girl $girl
     */
    public function girlSay(Girl $girl)
    {
        $girl->say();
    }

    /**
     * Human 接口类型约束
     * @param Human $obj
     */
    public function humanRun(Human $obj)
    {
        $obj->run();
    }
}

$obj = new Action();
$obj->boySay(new Boy());// a boy say
echo '<br>';
$obj->girlSay(new Girl());// a girl say
echo '<br>';
$obj->humanRun(new Boy());// a boy run
echo '<br>';
$obj->humanRun(new Girl());// a girl run

When the type constraint is a specific object Boy or Girl, only the required object can be passed in. When the type constraint is interface Human, you can pass in the class Boy or Girl that implements the interface.

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