From 71f02cd041e9c20d309686fcccf830a0f919f641 Mon Sep 17 00:00:00 2001
From: Heather Miller <heather.miller@epfl.ch>
Date: Thu, 1 Nov 2012 21:51:36 +0100
Subject: SI-6399 Adds API docs for Any and AnyVal

- Updates AnyVal docs to address value classes.
- Updates Any docs to address universal traits.
---
 src/library/scala/AnyVal.scala | 37 ++++++++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

(limited to 'src/library')

diff --git a/src/library/scala/AnyVal.scala b/src/library/scala/AnyVal.scala
index d637527b30..ebdc963946 100644
--- a/src/library/scala/AnyVal.scala
+++ b/src/library/scala/AnyVal.scala
@@ -9,8 +9,8 @@
 package scala
 
 /** `AnyVal` is the root class of all ''value types'', which describe values
- *  not implemented as objects in the underlying host system.  The value classes
- *  are specified in SLS 12.2.
+ *  not implemented as objects in the underlying host system. Value classes
+ *  are specified in Scala Language Specification, section 12.2.
  *
  *  The standard implementation includes nine `AnyVal` subtypes:
  *
@@ -21,9 +21,36 @@ package scala
  *
  *  Other groupings:
  *
- *  The ''subrange types'' are [[scala.Byte]], [[scala.Short]], and [[scala.Char]].
- *  The ''integer types'' include the subrange types as well as [[scala.Int]] and [[scala.Long]].
- *  The ''floating point types'' are [[scala.Float]] and [[scala.Double]].
+ *   - The ''subrange types'' are [[scala.Byte]], [[scala.Short]], and [[scala.Char]].
+ *   - The ''integer types'' include the subrange types as well as [[scala.Int]] and [[scala.Long]].
+ *   - The ''floating point types'' are [[scala.Float]] and [[scala.Double]].
+ *
+ * Prior to Scala 2.10, `AnyVal` was a sealed trait. Beginning with Scala 2.10,
+ * however, it is possible to define a subclass of `AnyVal` called a ''user-defined value class''
+ * which is treated specially by the compiler. Properly-defined user value classes provide a way
+ * to improve performance on user-defined types by avoiding object allocation at runtime, and by
+ * replacing virtual method invocations with static method invocations.
+ *
+ * User-defined value classes which avoid object allocation...
+ *
+ *   - must have a single, public `val` parameter that is the underlying runtime representation.
+ *   - can define `def`s, but no `val`s, `var`s, or nested `traits`s, `class`es or `object`s.
+ *   - typically extend no other trait apart from `AnyVal`.
+ *   - cannot be used in type tests or pattern matching.
+ *   - may not override `equals` or `hashCode` methods.
+ *
+ * A minimal example:
+ * {{{
+ *     class Wrapper(val underlying: Int) extends AnyVal {
+ *       def foo: Wrapper = new Wrapper(underlying * 19)
+ *     }
+ * }}}
+ *
+ * It's important to note that user-defined value classes are limited, and in some circumstances,
+ * still must allocate a value class instance at runtime. These limitations and circumstances are
+ * explained in greater detail in the [[http://docs.scala-lang.org/overviews/core/value-classes.html Value Classes Guide]]
+ * as well as in [[http://docs.scala-lang.org/sips/pending/value-classes.html SIP-15: Value Classes]],
+ * the Scala Improvement Proposal.
  */
 abstract class AnyVal extends Any with NotNull {
   def getClass(): Class[_ <: AnyVal] = null
-- 
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