davianspace_options

Enterprise-grade Options pattern for Dart and Flutter — conceptually equivalent to Microsoft.Extensions.Options but expressed idiomatically in Dart, with no reflection, no mirrors, and zero external dependencies.

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Features

Concept	Dart equivalent	Description
IOptions<T>	Options<T>	Singleton-cached access
IOptionsSnapshot<T>	OptionsSnapshot<T>	Scoped / per-scope fresh snapshot
IOptionsMonitor<T>	OptionsMonitor<T>	Live access + change notifications
IOptionsFactory<T>	OptionsFactory<T>	Factory pipeline with validation
IOptionsMonitorCache<T>	OptionsMonitorCache<T>	Per-name instance cache
IConfigureOptions<T>	ConfigureOptions<T>	Configure registrations
IPostConfigureOptions<T>	PostConfigureOptions<T>	Post-configure registrations
IValidateOptions<T>	ValidateOptions<T>	Validation registrations
Named options	OptionsBuilder.configureNamed()	Per-name configuration branches
IChangeToken	ChangeToken	Change propagation primitives

---

Installation

dependencies:
  davianspace_options: ^1.0.3

---

Quick start

1 — Simple singleton options (Options<T>)

import 'package:davianspace_options/davianspace_options.dart';

class DatabaseOptions {
  String host = 'localhost';
  int    port = 5432;
}

void main() {
  final factory = OptionsFactoryImpl<DatabaseOptions>(
    instanceFactory: DatabaseOptions.new,
    configureOptions: [
      ConfigureNamedOptions(
        name: null, // applies to every name
        configure: (opts) {
          opts.host = 'db.example.com';
          opts.port = 5432;
        },
      ),
    ],
  );

  final options = OptionsManager<DatabaseOptions>(factory: factory);

  // Lazily created once, cached forever.
  final db = options.value;
  print(db.host); // db.example.com

  // Same physical instance on repeated access.
  assert(identical(options.value, db));
}

---

2 — Named options

final options = OptionsManager<DatabaseOptions>(factory: factory);

final primary = options.get('primary');
final replica  = options.get('replica');

// Different instances, independently configured.

---

3 — Validation

final factory = OptionsFactoryImpl<DatabaseOptions>(
  instanceFactory: DatabaseOptions.new,
  validators: [
    DelegateValidateOptions(
      name: null,
      validate: (name, opts) {
        if (opts.host.isEmpty) {
          return ValidateOptionsResult.fail('$name: host is required.');
        }
        return ValidateOptionsResult.success();
      },
    ),
  ],
);

try {
  factory.create(Options.defaultName); // throws if host is empty
} on OptionsValidationException catch (e) {
  for (final msg in e.failures) print(msg);
}

---

4 — Fluent builder

final builder = OptionsBuilder<DatabaseOptions>(factory: DatabaseOptions.new)
  ..configure((opts) => opts.host = 'db.example.com')
  ..postConfigure((opts) => opts.port = opts.port == 0 ? 5432 : opts.port)
  ..validate(
    (name, opts) => opts.host.isNotEmpty
        ? ValidateOptionsResult.success()
        : ValidateOptionsResult.fail('$name: host required'),
  );

final factory = OptionsFactoryImpl<DatabaseOptions>(
  instanceFactory: builder.factory,
  configureOptions:     builder.configureActions,
  postConfigureOptions: builder.postConfigureActions,
  validators:           builder.validators,
);

---

5 — Live change notifications (OptionsMonitor<T>)

final notifier = OptionsChangeNotifier();

final monitor = OptionsMonitorImpl<DatabaseOptions>(
  factory:  factory,
  notifier: notifier,
);

final registration = monitor.onChange((opts, name) {
  print('$name changed → host=${opts.host}');
});

// Trigger a reload from your app (file watcher, remote config, etc.):
notifier.notifyChange(Options.defaultName);

// Always dispose when done:
registration.dispose();
monitor.dispose();

---

6 — Scoped snapshot (OptionsSnapshot<T>)

Create one OptionsManager per logical scope (request, unit-of-work, test) to get a fresh snapshot that remains stable within that scope:

void handleRequest(OptionsFactory<FeatureFlags> factory) {
  // New manager = new scope; instances are created fresh from the factory.
  final snapshot = OptionsManager<FeatureFlags>(factory: factory);

  final flags  = snapshot.value;         // cached within this scope
  final beta   = snapshot.get('beta');   // independent named snapshot

  // ... use flags ...
}

---

7 — DI container integration (davianspace_dependencyinjection)

When used with davianspace_dependencyinjection, the Options Pattern is wired into the container via fluent extension methods that automatically register Options<T>, OptionsSnapshot<T>, and OptionsMonitor<T> at the correct lifetimes.

# pubspec.yaml
dependencies:
  davianspace_options: ^1.0.3
  davianspace_dependencyinjection: ^1.0.3

import 'package:davianspace_options/davianspace_options.dart';
import 'package:davianspace_dependencyinjection/davianspace_dependencyinjection.dart';

class DatabaseOptions {
  String host = 'localhost';
  int    port = 5432;
}

final provider = ServiceCollection()
  ..configure<DatabaseOptions>(
    factory: DatabaseOptions.new,
    configure: (opts) {
      opts.host = 'db.prod.internal';
      opts.port = 5432;
    },
  )
  ..postConfigure<DatabaseOptions>((opts) {
    if (opts.host.isEmpty) throw ArgumentError('host is required');
  })
  .buildServiceProvider();

// Inject by interface — DI handles lifetime automatically.
final opts      = provider.getRequired<Options<DatabaseOptions>>().value;
final snapshot  = provider.getRequired<OptionsSnapshot<DatabaseOptions>>().value;
final monitor   = provider.getRequired<OptionsMonitor<DatabaseOptions>>();

// Live reload — signal the keyed notifier registered for the options type.
final notifier =
    provider.getRequiredKeyed<OptionsChangeNotifier>(DatabaseOptions);
notifier.notifyChange(Options.defaultName);

Lifetimes registered automatically:

Injectable type	Lifetime
Options<T>	Singleton
OptionsSnapshot<T>	Scoped
OptionsMonitor<T>	Singleton

---

Architecture

┌────────────────────────────────────────────────────────────────┐
│  Application layer                                             │
│  OptionsManager  •  OptionsMonitorImpl  •  OptionsBuilder      │
├────────────────────────────────────────────────────────────────┤
│  Factory pipeline                                              │
│  OptionsFactoryImpl                                            │
│    1. instantiate  →  2. configure  →  3. postConfigure        │
│    4. validate  →  (throws OptionsValidationException)         │
├────────────────────────────────────────────────────────────────┤
│  Cache layer                                                   │
│  OptionsMonitorCacheImpl  (per-name Map, O(1) lookup)          │
├────────────────────────────────────────────────────────────────┤
│  Change tracking                                               │
│  ManualChangeToken  •  CompositeChangeToken  •                 │
│  NeverChangeToken   •  OptionsChangeNotifier                   │
└────────────────────────────────────────────────────────────────┘

---

Migration notes from Microsoft.Extensions.Options

.NET API	Dart equivalent
services.AddOptions<T>()	OptionsBuilder<T>(factory: T.new)
.Configure<T>(action)	builder.configure(action)
.Configure<T>(name, action)	builder.configureNamed(name, action)
.PostConfigure<T>(action)	builder.postConfigure(action)
.ValidateDataAnnotations()	builder.validate(closureValidator)
IOptions<T>.Value	OptionsManager<T>.value
IOptionsSnapshot<T>.Get(name)	OptionsManager<T>.get(name)
IOptionsMonitor<T>.CurrentValue	OptionsMonitorImpl<T>.currentValue
IOptionsMonitor<T>.OnChange(cb)	monitor.onChange(cb) → disposable
IOptionsMonitorCache<T>.Clear()	OptionsMonitorCacheImpl<T>.clear()
IChangeToken	ChangeToken
CancellationTokenSource	ManualChangeToken

Key differences:

• No reflection or code generation – register a factory closure instead of relying on Activator.CreateInstance.
• No DI container coupling – the library is container-agnostic; wire it into GetIt, Riverpod, or any other solution.
• Disposal is explicit – call monitor.dispose() and registration.dispose() rather than relying on IDisposable from a DI container lifetime scope.
• Scoped snapshot via new instance – create a new OptionsManager per scope instead of registering with Scoped lifetime.

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Performance

• O(1) retrieval after first creation (hash-map backed cache).
• No reflection, no dart:mirrors.
• Factory closures — zero-cost compared to activator pattern.
• Listener list is a plain List<Function>; add/remove are O(n) but lists are tiny in practice.

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License

MIT — see LICENSE.