Re: How to find the type of an Option

Hi Tim,
I think you would need than an HList implementation. Miles Sabin has
one in his shapeless project: https://github.com/milessabin/shapeless
Hth Andreas

On Jan 2, 10:23 am, Tim Pigden wrote:
> Wow :-)
> Is there a limit to the maximum number of parameters I can cope with
> using this technique? Some of my records go past the length of normal
> tuples. Do I hit something before the case class limit of 21 or
> whatever it is?
>
> Tim
>
> On 1 January 2012 20:21, Derek Williams wrote:
>
>
>
>
>
> > How about this (no reflection required):
>
> > case class ProductOne(id: String, size: Option[Int])
>
> > case class ProductTwo(id: String, description: Option[String])
>
> > trait BuildFromXML[T] extends (xml.NodeSeq => Option[T]) { def apply(in:
> > xml.NodeSeq): Option[T] }
>
> > object BuildFromXML {
>
> >   implicit def buildString: BuildFromXML[String] = new BuildFromXML[String]
> > {
> >     def apply(in: xml.NodeSeq): Option[String] = in.headOption map (_.text)
> >   }
>
> >   implicit def buildInt: BuildFromXML[Int] = new BuildFromXML[Int] {
> >     def apply(in: xml.NodeSeq): Option[Int] = try { in.headOption map
> > (_.text.toInt) } catch { case _: NumberFormatException => None }
> >   }
>
> >   implicit def buildOption[A](implicit builder: BuildFromXML[A]):
> > BuildFromXML[Option[A]] = new BuildFromXML[Option[A]] {
> >     def apply(in: xml.NodeSeq): Option[Option[A]] = Some(builder(in))
> >   }
>
> >   implicit def buildTuple2[A, B](implicit buildA: BuildFromXML[A], buildB:
> > BuildFromXML[B]): BuildFromXML[(A, B)] = new BuildFromXML[(A, B)] {
> >     def apply(in: xml.NodeSeq): Option[(A, B)] = {
> >       for {
> >         a <- buildA(in \ "one")
> >         b <- buildB(in \ "two")
> >       } yield (a, b)
> >     }
> >   }
>
> >   implicit def buildTuple3[A, B, C](implicit buildA: BuildFromXML[A],
> > buildB: BuildFromXML[B], buildC: BuildFromXML[C]): BuildFromXML[(A, B, C)] =
> > new BuildFromXML[(A, B, C)] {
> >     def apply(in: xml.NodeSeq): Option[(A, B, C)] = {
> >       for {
> >         a <- buildA(in \ "one")
> >         b <- buildB(in \ "two")
> >         c <- buildC(in \ "three")
> >       } yield (a, b, c)
> >     }
> >   }
>
> >   def apply[T](in: xml.NodeSeq)(implicit builder: BuildFromXML[T]):
> > Option[T] = builder(in)
>
> >   def apply[A,B](fn: (A) => B, in: xml.NodeSeq)(implicit builder:
> > BuildFromXML[A]): Option[B] = builder(in) map fn
>
> >   def apply[A,B,C](fn: (A, B) => C, in: xml.NodeSeq)(implicit builder:
> > BuildFromXML[(A, B)]): Option[C] = builder(in) map fn.tupled
>
> >   def apply[A,B,C,D](fn: (A, B, C) => D, in: xml.NodeSeq)(implicit builder:
> > BuildFromXML[(A, B, C)]): Option[D] = builder(in) map fn.tupled
>
> > }
>
> > val xml1 = the string45
> > val xml2 = the string
> > val xml3 =
> > val xml4 = the stringthe
> > description
>
> > assert(BuildFromXML(ProductOne, xml1) == Some(ProductOne("the string",
> > Some(45))))
> > assert(BuildFromXML(ProductOne, xml2) == Some(ProductOne("the string",
> > None)))
> > assert(BuildFromXML(ProductOne, xml3) == None)
> > assert(BuildFromXML(ProductTwo, xml4) == Some(ProductTwo("the string",
> > Some("the description"))))
> > assert(BuildFromXML(ProductOne, xml4) == Some(ProductOne("the string",
> > None)))
>
> > --
> > Derek Williams
>
> --
> Tim Pigden
> Optrak Distribution Software Limited+44 (0)1992 517100http://www.linkedin.com/in/timpigdenhttp://optrak.com
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