In a PHP class, how can I make it so that the variables are a specific type?

Question

I have a PHP class, and I would like for it to have it so the variable is only a boolean?

class TestClass {
    private $isTrue;

    public function __construct ( $isTrue) {
        $this -> isTrue = $isTrue;
    }

    public function getIsTrue ($isTrue) {
        return $this -> isTrue;
    }

    public function setIsTrue ($isTrue) {
        $this -> isTrue = $isTrue;
    }
}

Or is it something that I am required to do in the setter and constructor like this?

class TestClass {
    private $isTrue;

    public function __construct ( $isTrue) {
        $this -> isTrue = (bool)$isTrue;
    }

    public function getIsTrue ($isTrue) {
        return $this -> isTrue;
    }

    public function setIsTrue ($isTrue) {
        $this -> isTrue = (bool)$isTrue;
    }
}

Answer 1

Yes, in PHP < 7, you have to do this manually, as you have done.

However, in PHP 7, you can use scalar typehinting to accomplish the same purpose:

<?php
class TestClass {
    private $isTrue;

    public function __construct(bool $isTrue) {
        $this->isTrue = $isTrue;
    }

    public function getIsTrue() {
        return $this->isTrue;
    }

    public function setIsTrue(bool $isTrue) {
        $this->isTrue = $isTrue;
    }
}

$tc = new TestClass(true);
var_dump($tc->getIsTrue()); //true

$tc->setIsTrue(false);
var_dump($tc->getIsTrue()); //false

$tc->setIsTrue(1);
var_dump($tc->getIsTrue()); //true

You can also enable strict-types mode, and the last case will throw an error:

<?php
declare(strict_types=1);

// ...same code here ...

$tc->setIsTrue(1);
var_dump($tc->getIsTrue());

Will produce:

Fatal error: Uncaught TypeError: Argument 1 passed to TestClass::setIsTrue() must be of the type boolean, integer given, called in /.../sth.php on line 27 and defined in /.../sth.php:16