putIfAbsent method

@override Future<bool> putIfAbsent(String key, T value, { CacheEntryDelegate<T>? delegate, })

Associates the specified key with the given value if not already associated with a value.

• key: key with which the specified value is to be associated
• value: value to be associated with the specified key
• delegate: provides the caller a way of changing the CacheEntry before persistence

Returns true if a value was set.

Implementation

@override
Future<bool> putIfAbsent(String key, T value,
    {CacheEntryDelegate<T>? delegate}) {
  // Current time
  final now = clock.now();
  // #region Statistics
  Stopwatch? watch;
  Future<CacheInfo?> Function(CacheInfo? info) posGet =
      (CacheInfo? info) => Future.value(info);
  Future<bool> Function(bool ok) posPut = (bool ok) => Future<bool>.value(ok);
  if (statsEnabled) {
    watch = clock.stopwatch()..start();
    posGet = (CacheInfo? info) {
      if (info == null || info.isExpired(now)) {
        stats.increaseMisses();
      } else {
        stats.increaseGets();
      }

      return Future.value(info);
    };
    posPut = (bool ok) {
      if (ok) {
        stats.increasePuts();
      }
      if (watch != null) {
        stats.addPutTime(watch.elapsedMicroseconds);
        watch.stop();
      }

      return Future<bool>.value(ok);
    };
  }
  // #endregion

  // Try to get the entry from the cache
  return _getStorageInfo(key).then(posGet).then((info) {
    final expired = info != null && info.isExpired(now);

    // If the entry exists on cache but is already expired we remove it first
    final pre = expired
        ? _removeStorageEntry(key, CacheEntryExpiredEvent<T>(this, info))
        : Future<void>.value();

    // If the entry is expired or non existent
    if (info == null || expired) {
      return pre
          .then((_) =>
              _newEntry(_entryBuilder(key, value, now, delegate: delegate)))
          .then(posPut);
    }

    return posPut(false);
  });
}