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Lift Framework example source code file (Merge.scala)

This example Lift Framework source code file (Merge.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lift Framework tags/keywords

a, b, b, jarray, jfield, jfield, jobject, jvalue, jvalue, list, list, mergedep, mergesyntax, r

The Lift Framework Merge.scala source code

/*
 * Copyright 2009-2010 WorldWide Conferencing, LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.liftweb
package json

/** Use fundep encoding to improve return type of merge function 
 *  (see: http://www.chuusai.com/2011/07/16/fundeps-in-scala/)
 *
 *  JObject merge JObject = JObject
 *  JArray  merge JArray  = JArray
 *  _       merge _       = JValue
 */
private [json] trait MergeDep[A <: JValue, B <: JValue, R <: JValue] {
  def apply(val1: A, val2: B): R
}

private [json] trait LowPriorityMergeDep {
  implicit def jjj[A <: JValue, B <: JValue] = new MergeDep[A, B, JValue] {
    def apply(val1: A, val2: B): JValue = merge(val1, val2)

    private def merge(val1: JValue, val2: JValue): JValue = (val1, val2) match {
      case (JObject(xs), JObject(ys)) => JObject(Merge.mergeFields(xs, ys))
      case (JArray(xs), JArray(ys)) => JArray(Merge.mergeVals(xs, ys))
      case (JField(n1, v1), JField(n2, v2)) if n1 == n2 => JField(n1, merge(v1, v2))
      case (f1: JField, f2: JField) => f2
      case (JNothing, x) => x
      case (x, JNothing) => x
      case (_, y) => y
    }
  }
}

private [json] trait MergeDeps extends LowPriorityMergeDep {
  implicit object ooo extends MergeDep[JObject, JObject, JObject] {
    def apply(val1: JObject, val2: JObject): JObject = JObject(Merge.mergeFields(val1.obj, val2.obj))
  }

  implicit object aaa extends MergeDep[JArray, JArray, JArray] {
    def apply(val1: JArray, val2: JArray): JArray = JArray(Merge.mergeVals(val1.arr, val2.arr))
  }
}

/** Function to merge two JSONs.
 */
object Merge {
  /** Return merged JSON.
   * <p>
   * Example:<pre>
   * val m = ("name", "joe") ~ ("age", 10) merge ("name", "joe") ~ ("iq", 105)
   * m: JObject(List(JField(name,JString(joe)), JField(age,JInt(10)), JField(iq,JInt(105))))
   * </pre>
   */
  def merge[A <: JValue, B <: JValue, R <: JValue]
    (val1: A, val2: B)(implicit instance: MergeDep[A, B, R]): R = instance(val1, val2)

  private[json] def mergeFields(vs1: List[JField], vs2: List[JField]): List[JField] = {
    def mergeRec(xleft: List[JField], yleft: List[JField]): List[JField] = xleft match {
      case Nil => yleft
      case JField(xn, xv) :: xs => yleft find (_.name == xn) match {
        case Some(y @ JField(yn, yv)) => 
          JField(xn, merge(xv, yv)) :: mergeRec(xs, yleft filterNot (_ == y))
        case None => JField(xn, xv) :: mergeRec(xs, yleft)
      }
    }

    mergeRec(vs1, vs2)
  }

  private[json] def mergeVals(vs1: List[JValue], vs2: List[JValue]): List[JValue] = {
    def mergeRec(xleft: List[JValue], yleft: List[JValue]): List[JValue] = xleft match {
      case Nil => yleft
      case x :: xs => yleft find (_ == x) match {
        case Some(y) => merge(x, y) :: mergeRec(xs, yleft filterNot (_ == y))
        case None => x :: mergeRec(xs, yleft)
      }
    }

    mergeRec(vs1, vs2)
  }

  private[json] trait Mergeable extends MergeDeps { 
    implicit def j2m[A <: JValue](json: A): MergeSyntax[A] = new MergeSyntax(json)

    class MergeSyntax[A <: JValue](json: A) {
      /** Return merged JSON.
       * @see net.liftweb.json.Merge#merge
       */
      def merge[B <: JValue, R <: JValue](other: B)(implicit instance: MergeDep[A, B, R]): R = 
        Merge.merge(json, other)(instance)
    }
  }
}

Other Lift Framework examples (source code examples)

Here is a short list of links related to this Lift Framework Merge.scala source code file:



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