【PHP】書記素クラスター単位でコールバックを適用する関数を定義する

まずは preg_replace_callback を使って定義する

<?php
$str = "ハ\u{309A}ハ\u{309A}";

var_dump(
  "パパ" === str_each_grapheme(
    $str, function($grapheme) { return normalizer_normalize($grapheme); })
);

<?php
function str_each_grapheme(string $str, callable $callback): string {
  $index = 0;
  return preg_replace_callback('/\X/su', function($matches) use ($callback, &$index) {
        ++$index;
        return $callback($matches[0], $index - 1);
    }, $str);
}

IntlBreakIterator を使った定義は次のとおり

function str_each_grapheme3(string $str, callable $callback): string {

  $it = IntlBreakIterator::createCharacterInstance();
  $it->setText($str);
  $current = 0;

  $ret = '';

  foreach ($it as $next) {
    if ($next === 0) {
      continue;
    }

    $size = $next - $current;
    $char = substr($str, $current, $size);
    $ret .= $callback($char);
    $current = $next;
  }

  return $ret;
}

grapheme_strlen、grapheme_substr を使った定義は次のとおり

function str_each_grapheme4(string $str, callable $callback): string {
  $size = grapheme_strlen($str);
  $ret = '';

  for ($i = 0; $i < $size; ++$i) {
    $g = grapheme_substr($str, $i, 1);
    $ret .= $callback($g);
  }

  return $ret;
}