Analysis

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Abstract FactoryAdapterBridgeBuilderChain of ResponsibilityCommandCompositeDecoratorFacadeFactory MethodFlyweightInterpreterIteratorMediatorMementoObserverPrototypeProxySingletonStateStrategyTemplate MethodVisitor

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Analysis

Pattern comparison

Reviewing 3 patterns.

Criteria
behavioralObserverView pattern
behavioralTemplate MethodView pattern
behavioralVisitorView pattern
Basics
Categorybehavioralbehavioralbehavioral
Summary———
IntentDefine a subscription mechanism so multiple observers can react to subject events without the subject knowing concrete subscriber details.Define the skeleton of an algorithm in a base class and let subclasses override selected steps without changing the overall structure.Separate an algorithm from the object structure it operates on by moving behavior into visitor objects.
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.Several classes share the same algorithm structure, but some steps need to vary between implementations.You need to perform operations across a set of different object types without stuffing all the logic into the objects themselves.
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
  • Relies on inheritance, which can be less flexible than composition in some designs
  • May create a deep class hierarchy if many variations are needed
  • 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
  • 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.Template Method is useful when you have repeated workflows with a common sequence of steps, such as processing orders, generating reports, and importing data.Visitor is useful for AST processing, reporting, cart calculations, and exporting object structures to alternate formats.