config: support p.lift(key) to optionally return a value
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		| @@ -6,9 +6,14 @@ class Field[T] | ||||
|  | ||||
| abstract class View { | ||||
|   final def apply[T](pname: Field[T]): T = apply(pname, this) | ||||
|   final def apply[T](pname: Field[T], site: View): T = find(pname, site).asInstanceOf[T] | ||||
|   final def apply[T](pname: Field[T], site: View): T = find(pname, site) match { | ||||
|     case Some(x) => x.asInstanceOf[T] | ||||
|   } | ||||
|  | ||||
|   protected[config] def find(pname: Any, site: View): Any | ||||
|   final def lift[T](pname: Field[T]): Option[T] = lift(pname, this) | ||||
|   final def lift[T](pname: Field[T], site: View): Option[T] = find(pname, site).map(_.asInstanceOf[T]) | ||||
|  | ||||
|   protected[config] def find(pname: Any, site: View): Option[Any] | ||||
| } | ||||
|  | ||||
| abstract class Parameters extends View { | ||||
| @@ -16,7 +21,7 @@ abstract class Parameters extends View { | ||||
|   final def alter(f: (View, View, View) => PartialFunction[Any,Any]): Parameters = Parameters(f) ++ this | ||||
|   final def alterPartial(f: PartialFunction[Any,Any]):                Parameters = Parameters((_,_,_) => f) ++ this | ||||
|  | ||||
|   protected[config] def chain(site: View, tail: View, pname: Any): Any | ||||
|   protected[config] def chain(site: View, tail: View, pname: Any): Option[Any] | ||||
|   protected[config] def find(pname: Any, site: View) = chain(site, new TerminalView, pname) | ||||
| } | ||||
|  | ||||
| @@ -37,8 +42,7 @@ class Config(p: Parameters) extends Parameters { | ||||
| // Internal implementation: | ||||
|  | ||||
| private class TerminalView extends View { | ||||
|   private class Unusable | ||||
|   def find(pname: Any, site: View): Any = pname match { case x: Unusable => () } | ||||
|   def find(pname: Any, site: View): Option[Any] = None | ||||
| } | ||||
|  | ||||
| private class ChainView(head: Parameters, tail: View) extends View { | ||||
| @@ -56,6 +60,6 @@ private class EmptyParameters extends Parameters { | ||||
| private class PartialParameters(f: (View, View, View) => PartialFunction[Any,Any]) extends Parameters { | ||||
|   protected[config] def chain(site: View, tail: View, pname: Any) = { | ||||
|     val g = f(site, this, tail) | ||||
|     if (g.isDefinedAt(pname)) g.apply(pname) else tail.find(pname, site) | ||||
|     if (g.isDefinedAt(pname)) Some(g.apply(pname)) else tail.find(pname, site) | ||||
|   } | ||||
| } | ||||
|   | ||||
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