Why so many change types for mutable vec?

[andrewbaxter]

I think all vec changes can be represented as a single splice tuple with an offset, remove count, and add list.

I was wondering why this has so many different vec change event types (push, pop, insert, etc).

[Pauan]

That would be less efficient, because Vec requires a heap allocation. The only time a heap allocation is necessary with VecDiff is with the Replace variant, which completely replaces all the old values with new values.

VecDiff is an internal implementation detail, so the primary goal is correctness, functionality, and performance. Simplicity is a nice bonus, but it is less important than those other goals.

[andrewbaxter]

Ah I see, and it only allows single-element changes (no extend/range delete). Thanks for answering!

[Pauan]

Yes, multiple changes are represented as multiple VecDiff.

Perhaps in the future I can add a new Splice variant that would use the Vec::splice method.

In practice I've never used Vec::splice, it doesn't seem to be very common.