Add section on auto-tupling of function parameters

Author: odersky

docs/docs/reference/auto-parameter-tupling.md

@@ -0,0 +1,33 @@
+---
+layout: doc-page
+title: "Automatic Tupling of Function Parameters"
+---
+
+Say you have a list of pairs
+
+     val xs: List[(Int, Int)]
+
+and you want to map `xs` to a list of `Int`s so that eich pair of numbers is mapped to
+their sum. Previously, the best way to do this was with a pattern-matching decomposition:
+
+    xs map {
+      case (x, y) => x + y
+    }
+
+While correct, this is also inconvenient. Dotty now also allows:
+
+    xs.map {
+      (x, y) => x + y
+    }
+
+or, equivalently:
+
+    xs.map(_ + _)
+
+Generally, a function value with `n > 1` parameters is converted to a
+pattern-matching closure using `case` if the expected type is a unary
+function type of the form `((T_1, ..., T_n)) => U`.
+
+
+
+

docs/docs/reference/desugarEnums.md

@@ -89,7 +89,7 @@ comma separated simple cases into a sequence of cases.
 
        case C <params> ...
 
-   expands analogous to a case class:
+   expands analogous to a final case class:
 
        final case class C <params> ...
 

docs/sidebar.yml

@@ -20,7 +20,9 @@ sidebar:
          -title: Multiversal Equality
           url: docs/reference/multiversal-equality.html
         - title: By-Name Implicits
-          url: docs/reference/implicit-by-name-parameters.html
+          url: docs/reference/implicit-by-name-parameters.htmldocs/reference/implicit-by-name-parameters.html
+        - title: Auto Parameter Tupling
+          url: docs/reference/auto-parameter-tupling.html
     - title: Usage
       subsection:
         - title: sbt-projects

tests/pos/reference/auto-param-tupling.scala

@@ -0,0 +1,17 @@
+package autoParamTupling {
+
+object t1 {
+  val xs: List[(Int, Int)] = ???
+
+  xs.map {
+    case (x, y) => x + y
+  }
+
+  xs.map {
+    (x, y) => x + y
+  }
+
+  xs.map(_ + _)
+
+}
+}