Analysis

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Abstract FactoryAdapterBridgeBuilderChain of ResponsibilityCommandCompositeDecoratorFacadeFactory MethodFlyweightInterpreterIteratorMediatorMementoObserverPrototypeProxySingletonStateStrategyTemplate MethodVisitor

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Analysis

Pattern comparison

Reviewing 3 patterns.

Criteria
behavioralObserverView pattern
structuralProxyView pattern
behavioralTemplate MethodView pattern
Basics
Categorybehavioralstructuralbehavioral
Summary———
IntentDefine a subscription mechanism so multiple observers can react to subject events without the subject knowing concrete subscriber details.Provide a surrogate or placeholder for another object to control access to it.Define the skeleton of an algorithm in a base class and let subclasses override selected steps without changing the overall structure.
Decision factors
ProblemA system needs to notify multiple dependent objects when state changes occur, but hardcoding those dependencies makes the design rigid and tightly coupled.A client needs to interact with an object indirectly because the real object may be expensive, sensitive, or remote.Several classes share the same algorithm structure, but some steps need to vary between implementations.
Tradeoffs
  • 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
  • Adds another layer of indirection
  • Can make the design more complex when the extra control is unnecessary
  • Relies on inheritance, which can be less flexible than composition in some designs
  • May create a deep class hierarchy if many variations are needed
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
  • Event-driven systems
  • Web
  • Backend
  • Mobile
  • UI kits
  • Cross-platform systems
  • Web
  • Backend
  • Mobile
  • UI kits
  • Cross-platform systems
Integration notesObservers work well inside a single application boundary for UI events, domain events, and in-process notifications where subscribers change dynamically.Proxy is useful for lazy loading, access control, caching, logging, and remote service wrappers.Template Method is useful when you have repeated workflows with a common sequence of steps, such as processing orders, generating reports, and importing data.