Analysis

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Abstract FactoryAdapterBridgeBuilderChain of ResponsibilityCommandCompositeDecoratorFacadeFactory MethodFlyweightInterpreterIteratorMediatorMementoObserverPrototypeProxySingletonStateStrategyTemplate MethodVisitor

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Analysis

Pattern comparison

Reviewing 3 patterns.

Criteria
structuralCompositeView pattern
structuralDecoratorView pattern
behavioralObserverView pattern
Basics
Categorystructuralstructuralbehavioral
SummaryCompose objects into tree structures to represent part-whole hierarchies and let clients work with individual and composite objects through the same interface.Wrap an object with other objects that implement the same contract so responsibilities can be layered dynamically.—
IntentCompose objects into tree structures to represent part-whole hierarchies and let clients work with individual and composite objects through the same interface.Wrap an object with other objects that implement the same contract so responsibilities can be layered dynamically.Define a subscription mechanism so multiple observers can react to subject events without the subject knowing concrete subscriber details.
Decision factors
ProblemA system needs to treat individual objects and groups of objects uniformly, but the hierarchy becomes difficult to manage with separate code paths.A system needs to add optional behaviors to an object without creating many subclasses for every feature combination.A system needs to notify multiple dependent objects when state changes occur, but hardcoding those dependencies makes the design rigid and tightly coupled.
Tradeoffs
  • Can make the design more abstract and harder to follow.
  • May require careful handling of operations that only apply to some nodes in the tree.
  • Makes recursive tree operations and client code much simpler.
  • Can introduce many small wrapper classes that are harder to trace in debugging.
  • Ordering of decorators matters, so composition needs to be deliberate.
  • Keeps responsibilities modular and easy to combine.
  • Notification flows can become hard to trace when many observers react to the same event
  • Observers may receive updates they do not need unless subscriptions are carefully designed
Practical fit
Languages
  • typescript
  • java
  • python
  • angular
  • react
  • react-native
  • csharp
  • dotnet
  • typescript
  • java
  • python
  • angular
  • react
  • react-native
  • csharp
  • dotnet
  • typescript
  • java
  • python
  • angular
  • react
  • react-native
  • csharp
  • dotnet
Platforms
  • web
  • backend
  • mobile
  • ui kits
  • cross-platform systems
  • frontend
  • backend
  • services
  • Web
  • Backend
  • Event-driven systems
Integration notesComposite is useful when a hierarchy of nested objects should expose a common interface, such as files and folders, menus and submenus, org charts, widget trees, or scene graphs.Decorators work well for cross-cutting concerns such as logging, retry, caching, compression, and telemetry because each layer keeps the same interface while adding one concern.Observers work well inside a single application boundary for UI events, domain events, and in-process notifications where subscribers change dynamically.