exercism-php/list-ops/ListOps.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);

class ListOps {

  public function append(array $list1, array $list2): array {
    $list = $list1;
    foreach ($list2 as $item) {
      $list[] = $item;
    }
    return $list;
  }

  public function concat(array $list1, array ...$listn): array {
    $res = $list1;
    foreach ($listn as $list) {
      foreach ($list as $item) {
        $res[] = $item;
      }
    }
    return $res;
  }

  /**
   * @param callable(mixed $item): bool $predicate
   */
  public function filter(callable $predicate, array $list): array {
    return array_values(array_filter($list, $predicate));
  }

  public function length(array $list): int {
    return count($list);
  }

  /**
   * @param callable(mixed $item): mixed $function
   */
  public function map(callable $function, array $list): array {
    return array_map($function, $list);
  }

  /**
   * @param callable(mixed $accumulator, mixed $item): mixed $function
   */
  public function foldl(callable $function, array $list, $accumulator) {
    return array_reduce($list, $function, $accumulator);
  }

  /**
   * @param callable(mixed $accumulator, mixed $item): mixed $function
   */
  public function foldr(callable $function, array $list, $accumulator) {
    return array_reduce(array_reverse($list), $function, $accumulator);
  }

  public function reverse(array $list): array {
    return array_reverse($list);
  }

}