Analysis

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Analysis

Pattern comparison

Reviewing 3 patterns.

Criteria
structuralFlyweightView pattern
behavioralStateView pattern
behavioralVisitorView 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.Allow an object to alter its behavior when its internal state changes by delegating state-specific behavior to separate state objects.Separate an algorithm from the object structure it operates on by moving behavior into visitor objects.
Decision factors
ProblemA system creates a large number of similar objects, but storing all of their state separately uses too much memory.An object behaves differently depending on its internal state, and conditional logic is becoming hard to manage.You need to perform operations across a set of different object types without stuffing all the logic into the objects themselves.
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
  • Can introduce many small classes if the state graph is large
  • State transitions may become harder to trace if spread across multiple classes
  • 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
  • Mobile
  • UI kits
  • Cross-platform 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.State is useful for workflows, media players, order lifecycles, and any domain where behavior changes as the object moves through a lifecycle.Visitor is useful for AST processing, reporting, cart calculations, and exporting object structures to alternate formats.