`calculateRecurrenceSet` return value is not accurate about ical4j

[raboof]

Let me know if you think there are advantages for your suggestion over this one.

Gladly!

This basically indicates there is no correlation between the period and the recurrence set, as the temporal type is derived from the type used in DTSTART property.

That makes sense to me.

Generally, I think a library should use the type system to specify what it guarantees. The user of the library can make additional assumptions, and the mechanism to encode those is casts. From that perspective, I think

public final Set<Period<Temporal>> calculateRecurrenceSet(Period<? extends Temporal> period)

would be slightly better. In

Set<Period<LocalDate>> result = calculateRecurrenceSet(period);
LocalDate date = result.iterator().next().getStart()

, when passing in events with different types for the DTSTART property, it would be surprising to me to get a ClassCastException on the second line. With my proposed signature, indeed this code becomes either

Set<Period<LocalDate>> result = (Set<Period<LocalDate>>) calculateRecurrenceSet(period);
LocalDate date = result.iterator().next().getStart()

or

Set<Period<Temporal>> result = calculateRecurrenceSet(period);
LocalDate date = (LocalDate) result.iterator().next().getStart()

While this is more verbose, I like how the cast makes it explicit that I'm responsible for this assumption (justified by the knowledge of the DTSTART property).

Anyway, I don't feel particularly strongly about this, and I'm happy with the library as it is, but since you asked these are my 2ct :)

[benfortuna]

Thanks for the feedback, apologies for late response.

This has been fixed in a recent version, although the fix is slightly different to your suggestion:

public final <T extends Temporal> Set<Period<T>> calculateRecurrenceSet(Period<? extends Temporal> period)

This basically indicates there is no correlation between the period and the recurrence set, as the temporal type is derived from the type used in DTSTART property.

The difference is that the caller can use their knowledge of the DTSTART property to assume the correct type, e.g:

Set<Period<LocalDate>> result = calculateRecurrenceSet(period);

Let me know if you think there are advantages for your suggestion over this one.

https://javadoc.io/doc/org.mnode.ical4j/ical4j/latest/ical4j.core/net/fortuna/ical4j/model/Component.html

[benfortuna]

Good points, although I think the explicit cast of the entire set doesn't work (I get following error):

Inconvertible types; cannot cast 'java.util.Set<net.fortuna.ical4j.model.Period<java.time.temporal.Temporal>>' to 'java.util.Set<net.fortuna.ical4j.model.Period<java.time.LocalDate>>'

Still, I might change it anyway.