Analysis

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Abstract FactoryAdapterBridgeBuilderChain of ResponsibilityCommandCompositeDecoratorFacadeFactory MethodFlyweightInterpreterIteratorMediatorMementoObserverPrototypeProxySingletonStateStrategyTemplate MethodVisitor

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Analysis

Pattern comparison

Reviewing 3 patterns.

Criteria
behavioralIteratorView pattern
behavioralObserverView pattern
behavioralVisitorView pattern
Basics
Categorybehavioralbehavioralbehavioral
Summary———
IntentProvide a way to access elements of an aggregate sequentially while hiding the underlying representation.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 collection needs to be traversed without exposing how it is stored internally.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 add extra classes and abstraction for simple collections
  • May be unnecessary when built-in language iteration is already enough
  • 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
  • Web
  • Backend
  • Mobile
  • UI kits
  • Cross-platform systems
  • Web
  • Backend
  • Event-driven systems
  • Web
  • Backend
  • Mobile
  • UI kits
  • Cross-platform systems
Integration notesIterator is useful for pagination, custom collections, ordered traversal, and any case where clients should not know the internal data structure.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.