PHP 7 - Why does a method that returns the primitive String type not generate an error when returning a Boolean value?

Question

PHP 7 - Why a method that returns the primitive type String, does not generate error when returning a value Boolean?

<?php

class Foo
{
    public function bar() : string
    {
        return true;
    }
}

$Foo = new Foo();
echo $Foo->bar();

?>

Output: 1

https://repl.it/repls/StraightBlondTag

Answer 1

By default all code in PHP has checking Weak, and to enable put a line at the top of the file including before the namespace that will ensure and check the types rigorously (checking Strong): (declare(strict_types = 1);):

<?php

    declare(strict_types = 1); // habilitando checagem forte

    class Foo
    {
        public function bar(): string
        {
            return true;
        }
    }

    $Foo = new Foo();
    echo ($Foo->bar());


?>

then it generates the erro:

Return value of Foo::bar() must be of the type string, boolean returned

Online Example

References:

• Strict Types and new declaration types in PHP 7
• PHP 7 - Return Type Declarations