Why should we always return values ​​from a function?

The function should not return anything ... If you look at the C (++) function, many of them are not (well, not explicitly):

void nonReturningFunction(const int *someParam);
int main()
{
    int i = 12;
    nonReturningFunction(&i);
    return 0;
}
void nonReturningFunction(const int *someParam)
{
    printf("I print the value of a parameter: %d",someParam);
}

The latter returns nothing, well, it returns the void. The main function returns something: 0it is usually a signal to the system so that it knows that the program is finished and it ended well.

PHP . , , -. , .

, :

<?php
    class Foo
    {
        private $foo,$bar;
        public function __construct()
        {
            $this->foo = 'bar';
        }
        public function getFoo()
        {
            return $this->foo;//<-- getter for private variable
        }
        public function getBar()
        {
            return $this->foo;//<-- getter for private variable
        }
        public function setBar($val = null)
        {
            $this->bar = $val;
            return $this;//<-- return instance for fluent interfacing
        }
        public function setFoo($val = null)
        {
            $this->foo = $val;
            return $this;
        }
    }
    $f = new Foo();
    $f->setFoo('foo')->setBar('bar');//<-- fluent interface
    echo $f->getFoo();
?>

setter , :

$f->setFoo('foo');
$f->setBar('Bar');

, . , :

function manipulateArray(array &$arr)//<-- pass by reference
{
    sort($arr);
}
$arr = range('Z','A');
manipulateArray($arr);
var_dump($arr);//array is sorted

:

function manipulateArray(array $arr)//<-- pass by copy
{
    sort($arr);
    return $arr;
}
$arr = range('Z','A');
manipulateArray($arr);
var_dump($arr);//array is not sorted!
$arr = manipulateArray($arr);//<-- requires reassign

, . , , . , , .