add init and size methods to NonEmptyList #1628
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| * }}} | ||
| */ | ||
| def init: List[A] = tail match { | ||
| case Nil => List.empty |
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Shouldn't this be head :: Nil?
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If the tail is empty the last element is the head, so the result is the empty list
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@peterneyens I added tests for init and size
Codecov Report
@@ Coverage Diff @@
## master #1628 +/- ##
==========================================
+ Coverage 93.37% 93.37% +<.01%
==========================================
Files 240 240
Lines 3937 3941 +4
Branches 139 144 +5
==========================================
+ Hits 3676 3680 +4
Misses 261 261
Continue to review full report at Codecov.
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| * scala> nel.last | ||
| * res0: Int = 5 | ||
| * }}} | ||
| */ | ||
| def last: A = tail.lastOption match { | ||
| case None => head | ||
| case Some(a) => a |
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tail.lastOption.getOrElse(head) might be more performant.
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he got the exact opposite advice from me a few days ago. Why do you say this? My understanding is that case class matching is very efficient and this also avoids the closure allocation (since getOrElse is by-name).
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@johnynek yeah, I forgot that getOrElse is by-name, and corrected myself in the other comment #1628 (comment)
| * res0: scala.collection.immutable.List[Int] = List(1, 2, 3, 4) | ||
| * }}} | ||
| */ | ||
| def init: List[A] = tail match { |
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@kailuowang any preference regarding init performance? toList.init is also an alternative
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I am going to stop pretend that I know anything about performance. I don't know if much difference can be made here.
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It (should) be more performant this way I think, because there's one less branch. But only very slightly.
| * }}} | ||
| */ | ||
| def last: A = tail.lastOption.getOrElse(head) | ||
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Please don't change this implementation. The one above avoids the allocation of the closure and was the motivation for writing it that way.
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ok. will revert
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oops, I forgot that getOrElse is by-name. 👅 we need a strict getOrElese.
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👍 from me after https://github.com/typelevel/cats/pull/1628/files#r112997682 is addressed. |
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