LateFuture - A Monad Type Thing That Doesn't Need The late Keyword

late_future.dart

import 'package:flutter/material.dart';
import 'package:nadz/nadz.dart';

typedef LateBuildContextFuture<T, T3> = LateFuture<T, BuildContext, T3>;

class LateFuture<T, T2, E> {
  LateFuture(
    this.getFuture,
    this.onError, {
    this.duration = const Duration(milliseconds: 1),
  });

  Future<T>? _future;

  final Future<T> Function(T2) getFuture;
  final E Function(Object error) onError;
  final Duration duration;

  Future<Result<T, E>> get future async {
    while (_future == null) {
      await Future<void>.delayed(duration);
    }

    switch (_future) {
      case null:
        return Error(onError(Exception('Future not initialized')));
      case final Future<T> f:
        try {
          final value = await f;
          return Success(value);
        } catch (e) {
          return Error(onError(e));
        }
    }
  }

  void initialize(T2 context) {
    if (_future != null) {
      return;
    }
    // ignore: discarded_futures
    _future = getFuture(context);
  }
}