How would you design a save game system?

What the interviewer wants to hear

• Decide what state to save; separate save data from runtime objects
• Serialise to a format like JSON or binary with a version number
• Use stable IDs to restore references
• Write safely: temp file then rename, backups
• Handle versioning/migration, platform storage and cloud saves

Model answer

I start by deciding exactly what needs saving, such as player stats, inventory, quest progress and world changes, and I keep it in plain save data classes, separate from GameObjects or Actors. Each saveable object has a stable unique ID so I can restore it and its references on load. I serialise to JSON during development because it is easy to read, and maybe a compact binary format for release. Every save file includes a version number, so when the game updates I can migrate old saves instead of breaking them. To avoid corruption if the game crashes during saving, I write to a temporary file and then rename it, and keep a backup. Finally I use each platform save API, support cloud saves, and test loading old saves in CI.

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