Analysis

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Analysis

Pattern comparison

Reviewing 3 patterns.

Criteria
structuralFlyweightView pattern
behavioralObserverView pattern
behavioralTemplate MethodView pattern
Basics
Categorystructuralbehavioralbehavioral
Summary———
IntentUse sharing to support large numbers of fine-grained objects efficiently by separating shared intrinsic state from per-object extrinsic state.Define 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.
Decision factors
ProblemA system creates a large number of similar objects, but storing all of their state separately uses too much memory.A 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.
Tradeoffs
  • Adds complexity because state must be split into shared and unshared parts
  • Can be harder to understand when many objects depend on an external context
  • 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
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 notesFlyweight is useful when thousands or millions of similar objects need to be represented efficiently, such as trees, glyphs, tiles, or UI tokens.Observers 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.