com.google.javascript.rhino.jstype.TernaryValue Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of closure-compiler Show documentation

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.

There is a newer version: v20240317

Show newest version

/*
 *
 * ***** 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;

/**
 * An enum for ternary logic. The {@link #TRUE} and {@link #FALSE} values
 * are equivalent to typical booleans, and the {@link #UNKNOWN} value plays the
 * role of a placeholder, which can be either {@link #TRUE} or
 * {@link #FALSE}.
 *
 * A ternary value expression evaluates to {@link #TRUE} or
 * {@link #FALSE} only if all replacements of {@link #UNKNOWN} in this
 * expression yield the same result. Therefore, the ternary logic coincides
 * with typical Boolean logic if the {@link #UNKNOWN} value is not
 * present in an expression.
 *
 * @see Ternary Logic
 */
public enum TernaryValue {
  /**
   * {@code false}
   */
  FALSE {
    @Override
    public TernaryValue and(TernaryValue that) {
      return FALSE;
    }

    @Override
    public TernaryValue not() {
      return TRUE;
    }

    @Override
    public TernaryValue or(TernaryValue that) {
      return that;
    }

    @Override
    public TernaryValue xor(TernaryValue that) {
      return that;
    }

    @Override
    public boolean toBoolean(boolean unknown) {
      return false;
    }

    @Override
    public String toString() {
      return "false";
    }
  },

  /**
   * {@code true}
   */
  TRUE {
    @Override
    public TernaryValue and(TernaryValue that) {
      return that;
    }

    @Override
    public TernaryValue not() {
      return FALSE;
    }

    @Override
    public TernaryValue or(TernaryValue that) {
      return TRUE;
    }

    @Override
    public TernaryValue xor(TernaryValue that) {
      return that.not();
    }

    @Override
    public boolean toBoolean(boolean unknown) {
      return true;
    }

    @Override
    public String toString() {
      return "true";
    }
  },

  /**
   * {@code unknown}, it represents lack of knowledge about whether this value
   * is {@code true} or {@code false}.
   */
  UNKNOWN {
    @Override
    public TernaryValue and(TernaryValue that) {
      return (FALSE.equals(that)) ? FALSE :  UNKNOWN;
    }

    @Override
    public TernaryValue not() {
      return UNKNOWN;
    }

    @Override
    public TernaryValue or(TernaryValue that) {
      return (TRUE.equals(that)) ? TRUE : UNKNOWN;
    }

    @Override
    public TernaryValue xor(TernaryValue that) {
      return UNKNOWN;
    }

    @Override
    public boolean toBoolean(boolean unknown) {
      return unknown;
    }

    @Override
    public String toString() {
      return "unknown";
    }
  };

  /**
   * Gets the {@code and} of {@code this} and {@code that}.
   */
  public abstract TernaryValue and(TernaryValue that);

  /**
   * Gets the {@code not} of {@code this}.
   */
  public abstract TernaryValue not();

  /**
   * Gets the {@code or} of {@code this} and {@code that}.
   */
  public abstract TernaryValue or(TernaryValue that);

  /**
   * Gets the {@code xor} of {@code this} and {@code that}.
   */
  public abstract TernaryValue xor(TernaryValue that);

  /**
   * Converts {@code this} ternary value to boolean. The {@code #TRUE} and
   * {@code #FALSE} values are simply converted to {@code true} and
   * {@code false} respectively, whilst the {@link #UNKNOWN} is converted
   * to the specified {@code unknown} value.
   *
   * @param unknown the boolean value to which the {@link #UNKNOWN} value is
   *     converted
   * @return return
   *     this == TRUE ? true :
   *     this == FALSE ? false :
   *     unknown
   */
  public abstract boolean toBoolean(boolean unknown);

  /**
   * Gets the TernaryValue for the given boolean.
   */
  public static TernaryValue forBoolean(boolean val) {
    return val ? TernaryValue.TRUE : TernaryValue.FALSE;
  }
}