exercism-php/pangram/Pangram.php

<?php

/*
 * By adding type hints and enabling strict type checking, code can become
 * easier to read, self-documenting and reduce the number of potential bugs.
 * By default, type declarations are non-strict, which means they will attempt
 * to change the original type to match the type specified by the
 * type-declaration.
 *
 * In other words, if you pass a string to a function requiring a float,
 * it will attempt to convert the string value to a float.
 *
 * To enable strict mode, a single declare directive must be placed at the top
 * of the file.
 * This means that the strictness of typing is configured on a per-file basis.
 * This directive not only affects the type declarations of parameters, but also
 * a function's return type.
 *
 * For more info review the Concept on strict type checking in the PHP track
 * <link>.
 *
 * To disable strict typing, comment out the directive below.
 */

declare(strict_types=1);

function buildLetters(): array {
  $letters = [];
  $base = ord('A');
  for ($i = 0; $i <= 25; $i++) {
    $letters[chr($base+$i)] = TRUE;
  }
  return $letters;
}

function isPangram(string $string): bool {
  $letters = buildLetters();
  foreach (mb_str_split(mb_strtoupper($string)) as $letter) {
    unset($letters[$letter]);
  }
  return empty($letters);
}