Packages

  • package root
    Definition Classes
    root
  • package net
    Definition Classes
    root
  • package liftweb
    Definition Classes
    net
  • package common
    Definition Classes
    liftweb
  • object HLists

    Basic support for heterogeneous lists, aka HLists.

    Basic support for heterogeneous lists, aka HLists.

    An HList can be constructed like so:

    import net.liftweb.common.HLists._

trait Base
case class Type1(value: String) extends Base
case class Type2(otherValue: String) extends Base

val myHList = Type1("Value") :+: Type2("Other Value") :+: HNil
myHList match {
  case firstThing :+: secondThing :+: HNil =>
    println(firstThing.value)
    println(secondThing.otherValue)
}

    Above, we see that the HList preserved the value of the types of its members, otherwise we wouldn't have been able to fetch value and otherValue, respectively.

    Trying the same thing with a list won't work:

    val myList = Type1("Value") :: Type2("Other Value") :: Nil
myList match {
  case firstThing :: secondThing :: Nil =>
    // error: value value is not a member of Product with Serializable with Base
    println(firstThing.value)
}

    This is because value is not defined in Base. The inferred type of the List has to be a common ancestor class or trait of Type1 and Type2, and no such type has a value method.

    Definition Classes
    common
  • :+:
  • HList
  • HListMethods
  • HNil

sealed trait HList extends AnyRef

The base trait for HLists. Functions that take HLists will need a type parameter subtype of HList:

def myHListFunction[T <: HList](list: HList) = {
  println(s"This HList has ${list.length} items!")
}
Linear Supertypes
AnyRef, Any
Known Subclasses
:+:, HNil
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