Memento Pattern

Memento Pattern captures the current state of an object and store it in such a way that you can retrieve it at a later time when you would like to return to the previous state.

Design overview

1. Originator. Allows object to be saved and restored. Object to be saved.
2. Memento. represents a stored state. Saved state
3. Care taker. requests a save from originator and receives a memento in response. Responsible for persistent the memento and retrieving the memento for the originator.

iOS apps typically use an Encoder to encode an originator’s state into a memento, and a Decoder to decode a memento back to an originator. This allows encoding and decoding logic to be reused across originators.

Use Codable, it is a typealias that combines Encoder and Decoder.

When should you use this pattern?

Save the state of an object and store. Allowing it to be retrieved at a later time and restore the previous state.

Use Cases

• Save game system (level, health, number of lives)
• Profile accounts

Be Careful with

Adding or removing codable properties, they can both throw an error. Mitigate this by expecting it to fail while doing a ‘try’.

Code Example - [Coming soon]

• iosdesignpatterns
• behavioralpatterns
• mementopattern