Add withDefault and atOrElse to replace None by a default value #886
Conversation
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Should this go into the |
Very good question. In theory, yes, but I am tempted to propose to soften our policy with regards to "lawfullness". I mean we should definitely document when an optic or combinator is a bit dodgy and maybe use a prefix/suffix to make it clear, but if it is really useful and the criteria for "lawfullness" are most often satisfied in real-world cases, then I think we should offer it. That's just my opinion, what do you think? and @yilinwei ? |
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Haskell lens has a similar but slightly different solution: https://hackage.haskell.org/package/lens-4.19.2/docs/Control-Lens-Combinators.html#v:non (if that linking doesn't work properly, the function you are looking for is eg (super useful for nested maps) They similarly note that it's not necessarily lawful ( The nested map situation in particular is why I'm SUPER keen on a solution to this :) |
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@TimWSpence correct, I believe I used the name |
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Oh sorry @julien-truffaut, I only looked at |
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Sorry, didn't see this earlier. I'm personally quite lax about coherence breakages in my own code (I've overridden an We should definitely make a note of the problems in the comment - but the any unexpected breakages I suspect is where people will property test the optic rather than anything else. I'm ambivalent on the whether to have a prefix/suffix. |
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I added tests and documentation for |
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| checkAll("fromIso", AtTests[MMap[Int, String], Int, Option[String]]) | ||
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| checkAll("ListMap", AtTests[ListMap[Int, String], Int, Option[String]]) | ||
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| test("atOrElse") { |
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Might be nice to have a test for nested maps? Obviously it should just work but given that it's one of the primary motivations for this, it might be nice to test it explicitly
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Actually, this might be better in AtExample if that is considered documentation of how to use it. Usage of at for nested maps is definitely not completely obvious at first
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Make sense. I am thinking to get rid of example module and instead use the website. It is probably easier to access.
| @@ -21,6 +23,36 @@ abstract class At[S, I, A] extends Serializable { | |||
| trait AtFunctions { | |||
| def at[S, I, A](i: I)(implicit ev: At[S, I, A]): Lens[S, A] = ev.at(i) | |||
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| /** | |||
| * Creates a Lens that zooms into an index `i` inside `S`. | |||
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It really is a pity that there isn't a better way to link documentation in scala. These examples feel as though they belong elsewhere.
This is a slightly unlawful
Isobut it is very convenient when you want to zoom into a Map like structure andset/modifythe value when the key doesn't exist.