Dart Design Patterns

A study project implementing the classic GoF (Gang of Four) design patterns in modern Dart 3 with sound null safety.

Each pattern lives in its own folder under lib/, with focused unit tests under test/. The file bin/main.dart contains a runnable demo of every pattern.

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Implemented patterns

Creational — lib/creational/

Pattern	Folder	Description
Singleton	lib/creational/singleton	Guarantees a single instance with a global access point.
Factory Method	lib/creational/factory	Creates currency objects based on a country, without exposing the instantiation logic.
Builder	lib/creational/builder	Step-by-step construction of a Pizza object with optional toppings.

Structural — lib/structural/

Pattern	Folder	Description
Adapter	lib/structural/adapter	Bridges a legacy LegacyPrinter to the modern ModernPrinter interface.
Bridge	lib/structural/bridge	Decouples a RemoteControl abstraction from TV/Radio implementations.
Decorator	lib/structural/decorator	Wraps ice creams with toppings, accumulating price dynamically.
Facade	lib/structural/facade	Hides the complexity of booting a computer (CPU + memory + hard drive) behind a single start().

Behavioral — lib/behavioral/

Pattern	Folder	Description
Command	lib/behavioral/command	Encapsulates light on/off requests as objects with undo support.
Chain of Responsibility	lib/behavioral/chain_of_responsibility	Routes authorization requests through a chain of role-based handlers.
Observer	lib/behavioral/observer	A singleton Subject (event bus) that notifies registered callbacks.
State	lib/behavioral/state	A media player whose play/pause behaviour changes with its state.
Strategy	lib/behavioral/strategy	Fighters with swappable kick/jump/punch behaviours.
Template Method	lib/behavioral/template_method	Skeleton for preparing hot beverages, with overridable steps and a hook.

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Getting started

Requires the Dart 3 SDK (>=3.0.0).

# install dependencies
dart pub get

# run the demo (all patterns)
dart run

# run the full test suite
dart test

# static analysis
dart analyze

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Project structure

dart_design_patterns/
├── bin/
│   └── main.dart                      # runnable demo of every pattern
├── lib/
│   ├── creational/                    # ── Creational patterns ──
│   │   ├── builder/                       # Builder
│   │   ├── factory/                       # Factory Method
│   │   └── singleton/                     # Singleton
│   ├── structural/                    # ── Structural patterns ──
│   │   ├── adapter/                       # Adapter
│   │   ├── bridge/                        # Bridge
│   │   ├── decorator/                     # Decorator
│   │   └── facade/                        # Facade
│   └── behavioral/                    # ── Behavioral patterns ──
│       ├── chain_of_responsibility/       # Chain of Responsibility
│       ├── command/                       # Command
│       ├── observer/                      # Observer / Subject
│       ├── state/                         # State
│       ├── strategy/                      # Strategy
│       └── template_method/               # Template Method
└── test/                              # unit tests (one file per pattern)

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Conventions

• Dart 3 with sound null safety (sdk: '>=3.0.0 <4.0.0').
• File names follow snake_case.dart.
• Linting via package:lints recommended rules.
• Tests use package:test.

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License

Released under the MIT License.