shapeless

问题 I encountered the following problem with implicits in Scala, using Shapeless's Generic.Aux : case class Complex(re: Double, im: Double) object Prod2 { def unapply[C, A, B](c: C)(implicit C: Generic.Aux[C, A :: B :: HNil]) = Some((C.to(c).head, C.to(c).tail.head)) } val c = Complex(1.0, 2.0) val Prod2(re, im) = c The code above does not compile. It reports Error:(22, 7) could not find implicit value for parameter C: shapeless.Generic.Aux[nexus.ops.Test.Complex,A :: B :: shapeless.HNil] val

问题 Problem: Let val v = List(0.5, 1.2, 0.3) model a realisation of some vector v = (v_1, v_2, v_3). The index j in v_j is implied by the element's position in the list. A lot of boilerplate and bugs have been due to tracking these indices, eg, when creating modified lists from the original. (How to make sure (in compile-time) that collection wasn't reordered? seems related.) General question: What could be a good way to ensure correct indexing at compile time? (I assume that performance is not

问题 (NOTE: split from Shapeless: Trying to restrict HList elements by their type and Shapeless: own HList constraint using Coproduct ) Question 3 - restrict case classes by parameter types A very nice additional gain would be, if I could use HList constraints to constrain case class only to be built from AnyVals, Strings, and a specific MyBaseTrait, that recursively fulfill the same constraint. The constraint being defined on the base trait and not to have to touch any derived case class would be

问题 (NOTE: split from Shapeless: Trying to restrict HList elements by their type and Shapeless: own HList constraint using Coproduct ) Question 3 - restrict case classes by parameter types A very nice additional gain would be, if I could use HList constraints to constrain case class only to be built from AnyVals, Strings, and a specific MyBaseTrait, that recursively fulfill the same constraint. The constraint being defined on the base trait and not to have to touch any derived case class would be

问题 I have auto-generated scala code using slick codegen. I see that some tables Rows are implements as HLists. (but these are slick HList, not the normal shapeless HList) Now I want a specific element from the HList returned as a Row by the slick query. I googled and found this thread Getting elements from an HList But this does not work for slick HList. it works very well for Shapeless HList I also tried the apply method val x : Long = slickHList(2) but this doesn't compile because type Any

问题 I have two shapeless extensible records, person and employee . The employee record is a subtype of person in some sense because it has all of the fields that person does and those fields are all subtypes of the corresponding fields in person : import shapeless._ ; import syntax.singleton._ ; import record._ val employeeId = ("first name" ->> "Jane") :: ("last name" ->> "Doe") :: ("title" ->> "software engineer") :: HNil val employee = ("id" ->> employeeId) :: ("city" ->> "San Francisco") :: (

问题 I have two shapeless extensible records, person and employee . The employee record is a subtype of person in some sense because it has all of the fields that person does and those fields are all subtypes of the corresponding fields in person : import shapeless._ ; import syntax.singleton._ ; import record._ val employeeId = ("first name" ->> "Jane") :: ("last name" ->> "Doe") :: ("title" ->> "software engineer") :: HNil val employee = ("id" ->> employeeId) :: ("city" ->> "San Francisco") :: (

问题 I'm fairly new to Shapeless, as one will infer from my question. Given an instance of LabelledGeneric , how do I get the name of the class that it represents. I can get the field name information from Keys , so I assume I need some other kind of Witness that encapsulates the type itself, but I cannot figure out which. Eg, if I have a case class called Foo in package com.bar, I want to get the string "com.bar.Foo" (or separately is fine). implicit def example[T, Repr <: HList](implicit label:

问题 In shapeless I'm trying to write a function such that takes two HLists l1 and l2 of arbitrary length which exhibit the following properties: Length of l1 and l2 are the same. l2 contains the exact types of l1 , wrapped in a constant outer type constructor. So, if l1 was 1 :: 1.2 :: "hello" :: HNil` l2 could be Ordering[Int] :: Ordering[Double] :: Ordering[String] :: HNil Using UnaryTCConstraint and LengthAux lets me constrain the lengths and require a static outer constructor for l2 , however

问题 I would like to create the equivalent of: def toTupleN[A1, ..., AN, L <: HList](l: L): TupleN[A1, ..., AN] Code using toTupleN should compile only when there is exactly one N combination of values in l that the tuple could be created from. Anything else should generate a compile-time error. Available implicit conversions should be taken into account. Note that there are no restrictions on the size of l or the ordering of values in it. Example: val l = 23 :: (1, "wibble") :: (2, "wobble") ::