Description:
------------
i suggest a scalar pseudo-type, much like Iterable,

today if one wants to accept scalar arguments, one has to write something like:

<?php
function f($sc){
    if(!is_string($sc) && !is_int($sc) && !is_float($sc) && !is_bool($sc)){
        throw new \InvalidArgumentException('argument #1 ($sc) must be a scalar type');
    }
}
class C{
    public $sc;
    function set_sc($sc){
        if(!is_string($sc) && !is_int($sc) && !is_float($sc) && !is_bool($sc)){
            throw new \InvalidArgumentException('argument #1 ($sc) must be a scalar type');
        }
        $this->sc = $sc;
    }
}
?>

luckily it gets easier in PHP8,

<?php
function f(string|int|float|bool $sc){

}
class C{
    public string|int|float|bool $sc
}
?>

even so, if there was a Scalar pseudo-type, i would use it.

Test script:
---------------
<?php
declare(strict_types=1);
function fun(Scalar $sc){
    var_dump($sc);
}
fun(1);

Expected result:
----------------
int(1)


Actual result:
--------------
Fatal error: Uncaught TypeError: fun(): Argument #1 ($sc) must be of type Scalar, int given, called in /in/PDjNq on line 6 and defined in /in/PDjNq:3
Stack trace:
#0 /in/PDjNq(6): fun(1)
#1 {main}
  thrown in /in/PDjNq on line 3

Process exited with code 255.