<?php

function one(...$a){
    print_r($a);
    two(...$a);
}

function two ($a,$b,$c){
    print_r(['a'=>$a, 'b'=>$b, 'c'=>$c]);
}

one('this is a', 'this is b', 'this is c', 'this is d');

// Result:
// Array ( [0] => this is a [1] => this is b [2] => this is c [3] => this is d )
// Array ( [a] => this is a [b] => this is b [c] => this is c )