Get first element of an array

first.php

<?php

//Get value of first element in array, without modifying the array
$first_value = array_shift(array_values($array));

//Get key of first element
$first_key = array_shift(array_keys($array));

Why not:

function array_first_value($array){
    $array = reset($array);
    return $array;
}

for the value?

This one works for the last value:

function array_last_value($array){
    $array = end($array);
    return $array;
}

I wonder what the speed difference is...