shapeless records ... current state of play ...

gistfile1.scala

Welcome to Scala version 2.10.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_21).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import shapeless._ ; import SingletonTypes._ ; import Record._
import shapeless._
import SingletonTypes._
import Record._

scala> :paste
// Entering paste mode (ctrl-D to finish)

val book =
  ("author" ->> "Benjamin Pierce") ::
  ("title"  ->> "Types and Programming Languages") ::
  ("id"     ->>  262162091) ::
  ("price"  ->>  44.11) ::
  HNil

// Exiting paste mode, now interpreting.

book: shapeless.::[String with shapeless.Record.KeyType[String("author"),String],shapeless.::[String with shapeless.Record.KeyType[String("title"),String],shapeless.::[Int with shapeless.Record.KeyType[String("id"),Int],shapeless.::[Double with shapeless.Record.KeyType[String("price"),Double],shapeless.HNil]]]] = Benjamin Pierce :: Types and Programming Languages :: 262162091 :: 44.11 :: HNil

scala> book("author")  // Note result type ...
res0: String = Benjamin Pierce

scala> book("title")   // Note result type ...
res1: String = Types and Programming Languages

scala> book("id")      // Note result type ...
res2: Int = 262162091

scala> book("price")   // Note result type ...
res3: Double = 44.11

scala> book.keys       // Key values are materialized from singleton types encoded in value type
res4: shapeless.::[String("author"),shapeless.::[String("title"),shapeless.::[String("id"),shapeless.::[String("price"),shapeless.HNil]]]] = author :: title :: id :: price :: HNil

scala> book.values
res5: shapeless.::[String,shapeless.::[String,shapeless.::[Int,shapeless.::[Double,shapeless.HNil]]]] = Benjamin Pierce :: Types and Programming Languages :: 262162091 :: 44.11 :: HNil

scala> val newPrice = book("price")+2.0
newPrice: Double = 46.11

scala> val updated = book +("price" ->> newPrice)  // Update an existing field
updated: shapeless.::[String with shapeless.Record.KeyType[String("author"),String],shapeless.::[String with shapeless.Record.KeyType[String("title"),String],shapeless.::[Int with shapeless.Record.KeyType[String("id"),Int],shapeless.::[shapeless.Record.FieldType[String("price"),Double],shapeless.HNil]]]] = Benjamin Pierce :: Types and Programming Languages :: 262162091 :: 46.11 :: HNil

scala> updated("price")
res6: Double = 46.11

scala> val extended = updated + ("inPrint" ->> true)  // Add a new field
extended: shapeless.::[String with shapeless.Record.KeyType[String("author"),String],shapeless.::[String with shapeless.Record.KeyType[String("title"),String],shapeless.::[Int with shapeless.Record.KeyType[String("id"),Int],shapeless.::[shapeless.Record.FieldType[String("price"),Double],shapeless.::[shapeless.Record.FieldType[String("inPrint"),Boolean],shapeless.HNil]]]]] = Benjamin Pierce :: Types and Programming Languages :: 262162091 :: 46.11 :: true :: HNil

scala> val noId = extended - "id"  // Removed a field
noId: shapeless.::[String with shapeless.Record.KeyType[String("author"),String],shapeless.::[String with shapeless.Record.KeyType[String("title"),String],shapeless.::[shapeless.Record.FieldType[String("price"),Double],shapeless.::[shapeless.Record.FieldType[String("inPrint"),Boolean],shapeless.HNil]]]] = Benjamin Pierce :: Types and Programming Languages :: 46.11 :: true :: HNil

scala> noId("id")  // Attempting to access a missing field is a compile time error
<console>:25: error: could not find implicit value for parameter selector: shapeless.FieldSelector[shapeless.::[String with shapeless.Record.KeyType[String("author"),String],shapeless.::[String with shapeless.Record.KeyType[String("title"),String],shapeless.::[shapeless.Record.FieldType[String("price"),Double],shapeless.::[shapeless.Record.FieldType[String("inPrint"),Boolean],shapeless.HNil]]]],String("id")]
              noId("id")
                  ^

scala>