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   * Copyright (c) 1999, 2017, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package openjdk.tools.javac.comp;
  
  import openjdk.tools.javac.tree.*;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  /** A class for environments, instances of which are passed as
   *  arguments to tree visitors.  Environments refer to important ancestors
   *  of the subtree that's currently visited, such as the enclosing method,
   *  the enclosing class, or the enclosing toplevel node. They also contain
   *  a generic component, represented as a type parameter, to carry further
   *  information specific to individual passes.
   *
   *  <p><b>This is NOT part of any supported API.
   *  If you write code that depends on this, you do so at your own risk.
   *  This code and its internal interfaces are subject to change or
   *  deletion without notice.</b>
   */
  public class Env<A> implements Iterable<Env<A>> {
  
      /** The next enclosing environment.
       */
      public Env<A> next;
  
      /** The environment enclosing the current class.
       */
      public Env<A> outer;
  
      /** The tree with which this environment is associated.
       */
      public JCTree tree;
  
      /** The enclosing toplevel tree.
       */
      public JCTree.JCCompilationUnit toplevel;
  
      /** The next enclosing class definition.
       */
      public JCTree.JCClassDecl enclClass;
  
      /** The next enclosing method definition.
       */
      public JCTree.JCMethodDecl enclMethod;
  
      /** A generic field for further information.
       */
      public A info;
  
      /** Is this an environment for evaluating a base clause?
       */
      public boolean baseClause = false;
  
      /** Create an outermost environment for a given (toplevel)tree,
       *  with a given info field.
       */
      public Env(JCTree tree, A info) {
          this.next = null;
          this.outer = null;
          this.tree = tree;
          this.toplevel = null;
          this.enclClass = null;
          this.enclMethod = null;
          this.info = info;
      }
  
      /** Duplicate this environment, updating with given tree and info,
       *  and copying all other fields.
       */
      public Env<A> dup(JCTree tree, A info) {
          return dupto(new Env<>(tree, info));
      }
  
      /** Duplicate this environment into a given Environment,
       *  using its tree and info, and copying all other fields.
       */
      public Env<A> dupto(Env<A> that) {
          that.next = this;
          that.outer = this.outer;
          that.toplevel = this.toplevel;
          that.enclClass = this.enclClass;
          that.enclMethod = this.enclMethod;
          return that;
      }
  
      /** Duplicate this environment, updating with given tree,
       *  and copying all other fields.
       */
      public Env<A> dup(JCTree tree) {
          return dup(tree, this.info);
      }
  
      /** Return closest enclosing environment which points to a tree with given tag.
       */
      public Env<A> enclosing(JCTree.Tag tag) {
          Env<A> env1 = this;
          while (env1 != null && !env1.tree.hasTag(tag)) env1 = env1.next;
          return env1;
      }
  
      @Override
      public String toString() {
          StringBuilder sb = new StringBuilder();
          sb.append("Env[").append(info);
          if (outer != null)
              sb.append(",outer=").append(outer);
          sb.append("]");
          return sb.toString();
      }
  
      public Iterator<Env<A>> iterator() {
          return new Iterator<Env<A>>() {
              Env<A> next = Env.this;
              public boolean hasNext() {
                  return next.outer != null;
              }
              public Env<A> next() {
                  if (hasNext()) {
                      Env<A> current = next;
                      next = current.outer;
                      return current;
                  }
                  throw new NoSuchElementException();
              }
              public void remove() {
                  throw new UnsupportedOperationException();
              }
          };
      }
  }
  