Analysis

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Abstract FactoryAdapterBridgeBuilderChain of ResponsibilityCommandCompositeDecoratorFacadeFactory MethodFlyweightInterpreterIteratorMediatorMementoObserverPrototypeProxySingletonStateStrategyTemplate MethodVisitor

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Analysis

Pattern comparison

Reviewing 3 patterns.

Criteria
structuralDecoratorView pattern
behavioralObserverView pattern
behavioralVisitorView pattern
Basics
Categorystructuralbehavioralbehavioral
SummaryWrap an object with other objects that implement the same contract so responsibilities can be layered dynamically.——
IntentWrap 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.Separate an algorithm from the object structure it operates on by moving behavior into visitor objects.
Decision factors
ProblemA 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.You need to perform operations across a set of different object types without stuffing all the logic into the objects themselves.
Tradeoffs
  • 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
  • Requires updating the visitor interface when new element types are added
  • Can be awkward if the object structure changes often
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
  • frontend
  • backend
  • services
  • Web
  • Backend
  • Event-driven systems
  • Web
  • Backend
  • Mobile
  • UI kits
  • Cross-platform systems
Integration notesDecorators 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.Visitor is useful for AST processing, reporting, cart calculations, and exporting object structures to alternate formats.