Fix finagle#62 (const readers)

README.md

@@ -151,7 +151,8 @@ Request Reader Monad
 
 A `FutureRequestReader` has return type `Future[A]` so it might be simply used as an additional monad-transformation in a top-level for-comprehension statement. This is dramatically useful when a service should fetch some params from a request before doing a real job (and not doing it at all if some of the params are not found/not valid).
 
-There are three common implementations of a `FutureRequestReader`:
+There are four common implementations of a `FutureRequestReader`:
+* `io.finch.request.ConstFutureParam` - fetches a const param
 * `io.finch.request.RequiredParam` - fetches required params within specified type
 * `io.finch.request.OptionalParam` - fetches optional params
 * `io.finch.request.ValidationRule` - fails if given predicate is false
@@ -232,7 +233,6 @@ val service = new Service[HttpRequest, JsonResponse] {
 * `Some[A]` if param is presented in the request and may be converted to a requested type `IntParam`, `LongParam` or `BooleanParam`. 
 * `None` otherwise.
 
-
 #### A `io.finch.request.ValidationRule(param, rule)(predicate)` 
 * returns `Future.Done` when predicate is `true`
 * throws `ValidationFailed` exception with `rule` and `param` fields
@@ -243,6 +243,9 @@ There is also a couple of empty request readers that raises `NoSuchElementExcept
 * `io.finch.request.NoFutureParams` implementing `FutureRequestReader[Nothing]`
 * `io.finch.request.NoParams` implementing `RequestReader[Nothing]`
 
+#### Const readers
+Readers that read const params are also available: `io.finch.request.ConstFutureParam` and `io.finch.request.ConstParam`.
+
 ### Multiple-Value Params
 All the readers have companion readers that can read multiple-value params `List[A]` instead of single-value params `A`. Multiple-value readers have `s` postfix in their names. So, `Param` has `Params`, `OptionalParam` has `OptipnalParams` and finally `RequiredParam` has `RequiredParams` companions. There are also typed versions for every reader, like `IntParams` or even `OptionalLongParams`.
 

project/Build.scala

@@ -11,7 +11,7 @@ object Finch extends Build {
 
   lazy val buildSettings = Seq(
     organization := "io",
-    version := "0.1.3",
+    version := "0.1.4",
     scalaVersion := "2.10.3"
   )
 

src/main/scala/io/finch/request/package.scala

@@ -110,6 +110,38 @@ package object request {
     def apply(req: HttpRequest) = throw new NoSuchElementException("Empty reader.")
   }
 
+  /**
+   * A const param.
+   */
+  object ConstFutureParam {
+
+    /**
+     * Creates a ''FutureRequestReader'' that reads given ''const'' param from
+     * the request.
+     *
+     * @return a const param value
+     */
+    def apply[A](const: A) = new FutureRequestReader[A] {
+      def apply(req: HttpRequest) = const.toFuture
+    }
+  }
+
+  /**
+   * A const param.
+   */
+  object ConstParam {
+
+    /**
+     * Creates a ''RequestReader'' that reads given ''const'' param from
+     * the request.
+     *
+     * @return a const param value
+     */
+    def apply[A](const: A) = new RequestReader[A] {
+      def apply(req: HttpRequest) = const
+    }
+  }
+
   private[this] object StringToNumberOrFail {
     def apply[A](param: String, rule: String)(number: => A) = new FutureRequestReader[A] {
       def apply(req: HttpRequest) =