4 ms·

Why would you need a copy method for an immutable record?

• TomSwirly 5y ago
  Python's dataclasses have a "make a copy with these fields changed" function that's rippingly useful for immutable records.
• etripe 5y ago
  When applying events, for instance. In F#, you could do: match msg with | IncreaseCounter cnt -> { model with Count = model.Count + cnt } | DecreaseCounter cnt -> { model with Count = model.Count - cnt } | ResetCounter -> { model with Count = 0 } | ChangeRubric name -> { model with Rubric = name, Count = 0 } The "with" says: copy the original record by value, but change these fields. For completeness' sake: F# also has implicit returns, so the bit between brackets is the function's return value.