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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Bob Jervis
 *   Google Inc.
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

package com.google.javascript.rhino.jstype;

import com.google.errorprone.annotations.ForOverride;
import javax.annotation.Nullable;

/**
 * A vistor for {@code JSType}s.
 *
 * During visitation, an instance may calculate a result value.
 */
public interface Visitor {
  /**
   * Bottom type's case.
   */
  T caseNoType(NoType type);

  /**
   * Enum element type's case.
   */
  T caseEnumElementType(EnumElementType type);

  /**
   * All type's case.
   */
  T caseAllType();

  /**
   * Boolean value type's case.
   */
  T caseBooleanType();

  /**
   * Bottom Object type's case.
   */
  T caseNoObjectType();

  /**
   * Function type's case.
   */
  T caseFunctionType(FunctionType type);

  /**
   * Object type's case.
   */
  T caseObjectType(ObjectType type);

  /**
   * Unknown type's case.
   */
  T caseUnknownType();

  /**
   * Null type's case.
   */
  T caseNullType();

  /**
   * Named type's case.
   */
  T caseNamedType(NamedType type);

  /**
   * Proxy type's case.
   */
  T caseProxyObjectType(ProxyObjectType type);

  /**
   * Number value type's case.
   */
  T caseNumberType();

  /** BigInt value type's case. */
  T caseBigIntType();

  /** String value type's case. */
  T caseStringType();

  /**
   * Symbol value type's case.
   */
  T caseSymbolType();

  /**
   * Void type's case.
   */
  T caseVoidType();

  /**
   * Union type's case.
   */
  T caseUnionType(UnionType type);

  /**
   * Templatized type's case.
   */
  T caseTemplatizedType(TemplatizedType type);

  /**
   * Template type's case.
   */
  T caseTemplateType(TemplateType templateType);

  /** A type visitor with a default behaviour. */
  public abstract class WithDefaultCase implements Visitor {

    /**
     * Called for all cases unless the specific case is overridden in the concrete subclass.
     *
     * {@code null} is passed iff the caller is a spcific case that has no {@code JSType}
     * argument, example {@link #caseAllType()}.
     */
    @ForOverride
    protected abstract T caseDefault(@Nullable JSType type);

    @Override
    public T caseNoType(NoType type) {
      return this.caseDefault(type);
    }

    @Override
    public T caseEnumElementType(EnumElementType type) {
      return this.caseDefault(type);
    }

    @Override
    public T caseAllType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseBooleanType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseNoObjectType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseFunctionType(FunctionType type) {
      return this.caseDefault(type);
    }

    @Override
    public T caseObjectType(ObjectType type) {
      return this.caseDefault(type);
    }

    @Override
    public T caseUnknownType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseNullType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseNamedType(NamedType type) {
      return this.caseDefault(type);
    }

    @Override
    public T caseProxyObjectType(ProxyObjectType type) {
      return this.caseDefault(type);
    }

    @Override
    public T caseNumberType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseBigIntType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseStringType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseSymbolType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseVoidType() {
      return this.caseDefault(null);
    }

    @Override
    public T caseUnionType(UnionType type) {
      return this.caseDefault(type);
    }

    @Override
    public T caseTemplatizedType(TemplatizedType type) {
      return this.caseDefault(type);
    }

    @Override
    public T caseTemplateType(TemplateType type) {
      return this.caseDefault(type);
    }
  }
}