Efficient Dart

01_async_caching.dart

import 'dart:async';

void main() {
  // We retrieve boolean value 3 times in the for-loop below and print it.
  for (var i = 1; i <= 3; i++) {
    print('Printing "$value" $i time.');
  }
}

/// Internal cache for our value.
bool _value;

/// Public getter for our value.
/// If there is no cached value we fetch it from `_getValueAsync` 
/// and update the cache.
bool get value {
  if (_value == null) {
    _getValueAsync().then((_) {
      print('Setting value to $_');
      _value = _;
    });
  }

  return _value;
}

// Assume to get our value we need to ask some external service.
// For simplicity here we just return a Future which gives us 
// the same effect.
Future<bool> _getValueAsync() => new Future.value(true);