Added productElementName to Product.

case class field names your heart desires. Review by odersky.

scala> case class Foo[T](kilroy: String, burma: List[T], shave:
Seq[Int]) defined class Foo

scala> Foo("was here", List('myanmar), Seq(25, 25))

res0: Foo[Symbol] = Foo(was here,List('myanmar),List(25, 25))

scala> 0 to 2 map (res0 productElementName _)
res1: IndexedSeq[String] = IndexedSeq(kilroy, burma, shave)

4 files changed, 28 insertions, 6 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/Definitions.scala b/src/compiler/scala/tools/nsc/symtab/Definitions.scala
index 9c3739aa91..11ec664904 100644
--- a/src/compiler/scala/tools/nsc/symtab/Definitions.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Definitions.scala
@@ -287,6 +287,7 @@ trait Definitions extends reflect.generic.StandardDefinitions {
     lazy val ProductRootClass: Symbol = getClass("scala.Product")
       def Product_productArity = getMember(ProductRootClass, nme.productArity)
       def Product_productElement = getMember(ProductRootClass, nme.productElement)
+      def Product_productElementName = getMember(ProductRootClass, nme.productElementName)
       def Product_productPrefix = getMember(ProductRootClass, nme.productPrefix)
       def Product_canEqual = getMember(ProductRootClass, nme.canEqual_)
 
diff --git a/src/compiler/scala/tools/nsc/symtab/StdNames.scala b/src/compiler/scala/tools/nsc/symtab/StdNames.scala
index b17728799b..0d9d98b934 100644
--- a/src/compiler/scala/tools/nsc/symtab/StdNames.scala
+++ b/src/compiler/scala/tools/nsc/symtab/StdNames.scala
@@ -314,6 +314,7 @@ trait StdNames extends reflect.generic.StdNames { self: SymbolTable =>
     val print = newTermName("print")
     val productArity = newTermName("productArity")
     val productElement = newTermName("productElement")
+    val productElementName = newTermName("productElementName")
     val productPrefix = newTermName("productPrefix")
     val readResolve = newTermName("readResolve")
     val sameElements = newTermName("sameElements")
diff --git a/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala b/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
index 2fcce5f5db..6a68ddc68c 100644
--- a/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
@@ -88,14 +88,16 @@ trait SyntheticMethods extends ast.TreeDSL {
       typer typed { DEF(method) === LIT(nargs) }
     }
 
-    def productElementMethod(accs: List[Symbol]): Tree = {
-      val symToTpe  = makeTypeConstructor(List(IntClass.tpe), AnyClass.tpe)
-      val method    = syntheticMethod(nme.productElement, 0, symToTpe)
+    /** Common code for productElement and productElementName
+     */
+    def perElementMethod(accs: List[Symbol], methodName: Name, resType: Type, caseFn: Symbol => Tree): Tree = {
+      val symToTpe  = makeTypeConstructor(List(IntClass.tpe), resType)
+      val method    = syntheticMethod(methodName, 0, symToTpe)
       val arg       = method ARG 0
-      val default   = List( DEFAULT ==> THROW(IndexOutOfBoundsExceptionClass, arg) )
+      val default   = List(DEFAULT ==> THROW(IndexOutOfBoundsExceptionClass, arg))
       val cases     =
         for ((sym, i) <- accs.zipWithIndex) yield
-          CASE(LIT(i)) ==> Ident(sym)
+          CASE(LIT(i)) ==> caseFn(sym)
 
       typer typed {
         DEF(method) === {
@@ -103,6 +105,11 @@ trait SyntheticMethods extends ast.TreeDSL {
         }
       }
     }
+    def productElementMethod(accs: List[Symbol]): Tree =
+      perElementMethod(accs, nme.productElement, AnyClass.tpe, x => Ident(x))
+
+    def productElementNameMethod(accs: List[Symbol]): Tree =
+      perElementMethod(accs, nme.productElementName, StringClass.tpe, x => Literal(x.name.toString))
 
     def moduleToStringMethod: Tree = {
       val method = syntheticMethod(nme.toString_, FINAL, makeNoArgConstructor(StringClass.tpe))
@@ -273,6 +280,7 @@ trait SyntheticMethods extends ast.TreeDSL {
             Product_productPrefix   -> (() => productPrefixMethod),
             Product_productArity    -> (() => productArityMethod(accessors.length)),
             Product_productElement  -> (() => productElementMethod(accessors)),
+            Product_productElementName  -> (() => productElementNameMethod(accessors)),
             Product_canEqual        -> (() => canEqualMethod)
           )
         }
diff --git a/src/library/scala/Product.scala b/src/library/scala/Product.scala
index 8521cf2437..417b87f191 100644
--- a/src/library/scala/Product.scala
+++ b/src/library/scala/Product.scala
@@ -20,7 +20,7 @@ package scala
  */
 trait Product extends Equals {
 
-  /** for a product <code>A(x_1,...,x_k)</code>, returns <code>x_(n+1)</code>
+  /** For a product <code>A(x_1,...,x_k)</code>, returns <code>x_(n+1)</code>
    *  for <code>0 &lt;= n &lt; k</code>
    *
    *  @param  n the index of the element to return
@@ -29,6 +29,18 @@ trait Product extends Equals {
    */
   def productElement(n: Int): Any
 
+  /** Returns the name of the field at the given index from the definition
+   *  of the class.
+   *
+   *  @param  n   the index of the element name to return
+   *  @throws     NoSuchElementException      if the name data is unavailable for any reason
+   *  @throws     IndexOutOfBoundsException   if the index is out of range
+   *  @return     a String representing the field name
+   */
+  def productElementName(n: Int): String =
+    // the method implementation is synthetic - if it is not generated we always throw.
+    throw new NoSuchElementException()
+
   /** return k for a product <code>A(x_1,...,x_k)</code>
    */
   def productArity: Int