function eat_apple($apple)
{
    return true;
}

function eat_apple()
{
    $apple = func_get_arg(0);
    return true;
}

<?php
function display ($a, $b, $c) {
    echo $a . " is " . $b . " " . $c;
}
?>

<?php
display ("Rock", "good", "boy");
- this will not throw any error.

display ("Rock", "good");
- this will throw fatal error.
?>

class a{
  function X(MyOBJ $obj){...}
}

class b extends a{
  function X(string $s,int $i){...}
}
class c extends b{
  function X(){...}
}

//not good, you can only send 3 strings
function merge_strings($s1, $s2, $s3){
     return $s1 . $s2 . $s3;
}

//good one
function merge_strings(){
   return join('',func_get_args());
}

-function eat_apple($apple)
+function eat_apple()
 {
+    $apple = func_get_arg(0);
     return true;
 }