Analysis

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Analysis

Pattern comparison

Reviewing 3 patterns.

Criteria
behavioralMementoView pattern
behavioralObserverView pattern
behavioralTemplate MethodView pattern
Basics
Categorybehavioralbehavioralbehavioral
Summary———
IntentCapture and externalize an object's state so it can be restored to a previous point in time.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
ProblemAn object's internal state must be saved and restored later without exposing its implementation details.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
  • Snapshots can consume memory if many states are stored.
  • Care must be taken to keep mementos immutable and hidden from outside code.
  • 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 notesMemento is useful for undo/redo, checkpoints, draft recovery, and any workflow where state history matters.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.