Analysis

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Abstract FactoryAdapterBridgeBuilderChain of ResponsibilityCommandCompositeDecoratorFacadeFactory MethodFlyweightInterpreterIteratorMediatorMementoObserverPrototypeProxySingletonStateStrategyTemplate MethodVisitor

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Analysis

Pattern comparison

Reviewing 3 patterns.

Criteria
structuralCompositeView pattern
behavioralObserverView pattern
behavioralStateView pattern
Basics
Categorystructuralbehavioralbehavioral
SummaryCompose objects into tree structures to represent part-whole hierarchies and let clients work with individual and composite objects through the same interface.——
IntentCompose objects into tree structures to represent part-whole hierarchies and let clients work with individual and composite objects through the same interface.Define a subscription mechanism so multiple observers can react to subject events without the subject knowing concrete subscriber details.Allow an object to alter its behavior when its internal state changes by delegating state-specific behavior to separate state objects.
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 notify multiple dependent objects when state changes occur, but hardcoding those dependencies makes the design rigid and tightly coupled.An object behaves differently depending on its internal state, and conditional logic is becoming hard to manage.
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.
  • 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
  • Can introduce many small classes if the state graph is large
  • State transitions may become harder to trace if spread across multiple classes
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 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.Observers work well inside a single application boundary for UI events, domain events, and in-process notifications where subscribers change dynamically.State is useful for workflows, media players, order lifecycles, and any domain where behavior changes as the object moves through a lifecycle.