mbeckerle commented on a change in pull request #394: URL: https://github.com/apache/incubator-daffodil/pull/394#discussion_r453890762
########## File path: daffodil-core/src/main/scala/org/apache/daffodil/dsom/walker/AbstractDSOMWalker.scala ########## @@ -0,0 +1,163 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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 org.apache.daffodil.dsom.walker + +import org.apache.daffodil.dpath.NodeInfo.PrimType + +trait CommonContextView { + def namespaces: scala.xml.NamespaceBinding +} + +trait TermView extends CommonContextView { + def isArray: Boolean + def isOptional: Boolean + def walkDSOM[T](walker: AbstractDSOMWalker[T]): Unit = { + walker.onTermBegin(this) + walker.onTermEnd(this) + } +} + +trait SimpleTypeView { + def primType: PrimType +} +trait ComplexTypeView { + def group: ModelGroupView +} + +trait ModelGroupView extends TermView { + def groupMembers: Seq[TermView] + override def walkDSOM[T](walker: AbstractDSOMWalker[T]): Unit = { + walker.onTermBegin(this) + this.groupMembers.foreach(_.walkDSOM(walker)) + walker.onTermEnd(this) + } +} + +trait ChoiceView extends ModelGroupView +trait SequenceView extends ModelGroupView +trait GroupRefView extends ModelGroupView { + def isHidden: Boolean + override def walkDSOM[T](walker: AbstractDSOMWalker[T]): Unit = if (!isHidden) super.walkDSOM(walker) +} + +trait ElementDeclView extends CommonContextView { + def isSimpleType: Boolean + def isComplexType: Boolean + def simpleType: SimpleTypeView + def complexType: ComplexTypeView + def hasDefaultValue: Boolean +} + +trait ElementBaseView extends ElementDeclView with TermView { + def name: String + override def walkDSOM[T](walker: AbstractDSOMWalker[T]): Unit = { + walker.onTermBegin(this) + if (isComplexType) { + walker.onTypeBegin(Right(complexType)) + complexType.group.walkDSOM(walker) + walker.onTypeBegin(Right(complexType)) + } else { + walker.onTypeBegin(Left(simpleType)) + walker.onTypeBegin(Left(simpleType)) + } + walker.onTermEnd(this) + } + +} + +trait RootView extends ElementBaseView + +/** + * A class designed to walk the internal representation of a DFDL Schema File. + * + * There are 2 main event handlers an implementing class has to worry about: one for Terms, and + * another for Types. These are called as the DSOM is walked. + * + * Though recursion is used here to define the walk, it is not advised to use recursion between + * these event handlers. Instead, consider a stack-like structure, as the DFDL Schema structure + * as well as the recursive method call structure can be represented by trees. + * @tparam T the return type of walkDSOMSchema and onWalkEnd. This should be a class used to + * represent the structure of the Schema. You could always make it Unit if you don't + * want these methods to return anything. + */ +abstract class AbstractDSOMWalker[T] { + + /** + * Method to be called on the beginning of the traversal. It is recommended to add some + * sort of wrapper element to a stack if you're doing a typical stack-based traversal. + * + * @param root the root element of the DFDL Schema + */ + protected def onWalkBegin(root: RootView): Unit + + /** + * Method to be called when the traversal concludes. It is recommended to put any post-processing + * and anything to tidy up the stack or the result here. + * + * @param root the root element of the DFDL Schema + * @return the result of the traversal + */ + protected def onWalkEnd(root: RootView): T + + /** + * Method to be called whenever any element that is a Term is encountered. + * This applies to Sequence, Choice, GroupRef, ElementBase, etc. + * + * It is highly recommended that, when implementing this method, you pattern match + * some of these different sub-types at some point to handle each accordingly. + * + * @param termElement the term element + */ + def onTermBegin(termElement: TermView): Unit Review comment: To make this java friendly, one would typically use a visiting pattern so that what we do in scala via a match on types becomes calling a method which is overloaded on types of a parameter. I think we'd have to try it to see how it works out. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
