Add take/takeRight/drop/dropRight to Chain #4694
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| @@ -308,13 +310,14 @@ sealed abstract class Chain[+A] extends ChainCompat[A] { | |||
| arg match { | |||
| case Wrap(seq) => | |||
| if (count == 1) { | |||
| lhs.append(seq.last) | |||
| seq.last +: rhs | |||
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this was the bug. The rest of the changes are just optimizations to the code or scalacheck improvements.
| } else { | ||
| // count > 1 | ||
| val taken = seq.take(count) | ||
| // we may have not takeped all of count |
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hmm, out of curiosity, "takeped" – is it a typo or some slang I'm just not aware of? I also see "takeping" down below, so I guess it is intentional...
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no, I did drop first and I did find and replace to take and then changed the code. So, this was dropped and dropping with s/drop/take/.
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Thank you, these methods are really nice addition to Chain! One thing to clarify: |
| if (newCount > 0) { | ||
| // we have to keep takeping on the rhs | ||
| go(newLhs, newCount, rhs, Chain.nil) |
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Shouldn't we eagerly exit with the newLhs if rhs.isEmpty == true?
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I don't think so, we have to check for empty anyway on the next call call of the loop. If we also check here we are checking twice. If we could ensure we never see Empty in the loop it would be worth it, but it would mean we would we have uglier code: we don't have a total match, we have one arm (Empty) that is unreachable. I don't think the performance win would be there and it would complicate the code.
What do you think?
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Okay, actually, I took this suggestion. I remembered we have NonEmpty so we can recurse on that instead, that naturally pushes the check up to the places you suggest.
I still don't think it's any faster (since the Empty was the final check and always a terminal condition), but at least it's nice to be clear in the recursion that we are only operating on NonEmptyChain.
| if (newCount > 0) { | ||
| // we have to keep takeping on the rhs | ||
| go(Chain.nil, newCount, lhs, newRhs) |
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Shouldn't we eagerly exit with the newRhs if lhs.isEmpty == true?
| if (newCount > 0) { | ||
| // we have to keep dropping on the rhs | ||
| go(newCount, rhs, Chain.nil) |
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Shouldn't we eagerly exit with the Empty if rhs.isEmpty == true?
I reached for drop on Chain and realized we never implemented it however, we could implement it and using internal structure it can be more efficient than using iterators/toList.