computation-with-assumed-keys.php

<?php
function computationWithAssumedKeys(array $array, array $necessaryKeys) {
    $missingKeys = array_diff($necessaryKeys, array_keys($array));
    if (!empty($missingKeys)) {
        $message = 'Computation failed due to missing key(s): ' . implode(', ', $missingKeys);
        throw new \RuntimeException($message);
    }

    // compute...
}