shapeless

问题 I want to merge the fields of two different case classes into a single case class. For example, if I have the following case classes: case class Test(name:String, questions:List[Question], date:DateTime) case class Answer(answers:List[Answers]) I want a concise shapeless way to merge both into: TestWithAnswers(name:String, questions:List[Question], date:DateTime, answers:List[Answer]). Is there a nice shapeless answer out there? 回答1: You can use shapeless Generic to do this. val t: Test = ???

问题 Thanks to https://github.com/milessabin/shapeless/wiki/Feature-overview:-shapeless-2.0.0 I understand how to zip shapeless HLists: Import some stuff from Shapeless 2.0.0-M1: import shapeless._ import shapeless.ops.hlist._ import syntax.std.tuple._ import Zipper._ Create two HLists: scala> val h1 = 5 :: "a" :: HNil h1: shapeless.::[Int,shapeless.::[String,shapeless.HNil]] = 5 :: a :: HNil scala> val h2 = 6 :: "b" :: HNil h2: shapeless.::[Int,shapeless.::[String,shapeless.HNil]] = 6 :: b ::

问题 I started out with something like this: def nonEmpty[A] = (msg: String) => (a: Option[A]) => a.toSuccess(msg) val postal: Option[String] = request.param("postal") val country: Option[String] = request.param("country") val params = (postal |> nonEmpty[String]("no postal" )).toValidationNel |@| (country |> nonEmpty[String]("no country")).toValidationNel params { (postal, country) => ... } Now I thought it would be nice to reduce the boilerplate for better readability and for not having to

问题 Question 1 - Basic LUBConstraints My first try playing around with existing LUBConstraints fails for missing evidence (see code block below). Any hint why? Isn't an empty list a valid list of longs? no element violates the constraint. import shapeless.ops.coproduct import shapeless.{::, :+:, Coproduct, HNil, HList} object testLUBConstraints { import shapeless.LUBConstraint._ // !!! see comment on question - this satisfies the implicit below!!! // implicit val hnilLUBForLong = new

问题 In a Play application I'm working on, I'm trying to improve our system for processing flags, some of which are meant to be persistent options as a user navigates our app via links. I'd like to use Shapeless to map from a definition of the option to its value, and also to synthesize new query parameter from only the ones marked to be propagated. I also want to be able to take advantage of Shapeless's Record functionality to get strongly typed dereferencing of the parameter values.

问题 'map' preserves the number of elements, so using it on a Tuple seems sensible. My attempts so far: scala> (3,4).map(_*2) error: value map is not a member of (Int, Int) (3,4).map(_*2) ^ scala> (3,4).productIterator.map(_*2) error: value * is not a member of Any (3,4).productIterator.map(_*2) ^ scala> (3,4).productIterator.map(_.asInstanceOf[Int]*2) res4: Iterator[Int] = non-empty iterator scala> (3,4).productIterator.map(_.asInstanceOf[Int]*2).toList res5: List[Int] = List(6, 8) It looks quite

问题 I want to find out if a particular class member is present in a given case class or not. Following does give me that answer, failing at compile time which is right. (credit to Travis Brown) scala> def getIntId[A, R <: HList](a: A)(implicit | gen: LabelledGeneric.Aux[A, R], | sel: Selector.Aux[R, Witness.`'id`.T, Int] | ): Int = sel(gen.to(a)) case class Foo(id: String) case class Bar(id: Int, name: String) scala> getIntId(Bar(123, "bar")) res3: Int = 123 scala> getIntId(Foo("12345")) <console

问题 I want to find out if a particular class member is present in a given case class or not. Following does give me that answer, failing at compile time which is right. (credit to Travis Brown) scala> def getIntId[A, R <: HList](a: A)(implicit | gen: LabelledGeneric.Aux[A, R], | sel: Selector.Aux[R, Witness.`'id`.T, Int] | ): Int = sel(gen.to(a)) case class Foo(id: String) case class Bar(id: Int, name: String) scala> getIntId(Bar(123, "bar")) res3: Int = 123 scala> getIntId(Foo("12345")) <console

问题 I want to find out if a particular class member is present in a given case class or not. Following does give me that answer, failing at compile time which is right. (credit to Travis Brown) scala> def getIntId[A, R <: HList](a: A)(implicit | gen: LabelledGeneric.Aux[A, R], | sel: Selector.Aux[R, Witness.`'id`.T, Int] | ): Int = sel(gen.to(a)) case class Foo(id: String) case class Bar(id: Int, name: String) scala> getIntId(Bar(123, "bar")) res3: Int = 123 scala> getIntId(Foo("12345")) <console

问题 I have the following setup, where I want to copy an instance of baseData into that of moreData : sealed trait baseData { def weight: Int def priority: Int } sealed trait moreData { def weight: Int def priority: Int def t: String def id: String } case class data1(override val weight: Int, override val priority: Int) extends baseData case class moreData1 (override val weight:Int, override val priority: Int, override val t: String, override val id: String)extends moreData So copying myData into