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Flutter – How can I only return an optional type if an input parameter is optional?

Is there a way I can use the magic of generics to write a function that returns an optional if the input is optional, otherwise both non-null?

For example, I have two functions that I want to combine into one.

static Timestamp dateToTimestamp(DateTime dateTime) {
  return Timestamp.fromDate(dateTime);
}

static Timestamp? dateToTimestampOptional(DateTime? dateTime) {
  return (dateTime == null) ? null : Timestamp.fromDate(dateTime);
}
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2

Answers


  1. 0

    Make the type as generic

      Timestamp? dateToTimestamp<T extends DateTime?>(T dateTime) {
     return (dateTime == null) ? null : Timestamp.fromDate(dateTime); 
  }
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  2. 0

    Here’s how you can combine the two functions into one using generics:

    T? dateToTimestamp<T extends DateTime?>(T? dateTime) {
  return dateTime?.toTimestamp();
}

    Usage:

    // With DateTime argument (non-null)
Timestamp timestamp = dateToTimestamp(DateTime.now());

// With DateTime? argument (optional)
DateTime? maybeDateTime;
Timestamp? maybeTimestamp = dateToTimestamp(maybeDateTime);
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