/*
 * Copyright (c) 2013, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * The Universal Permissive License (UPL), Version 1.0
 *
 * Subject to the condition set forth below, permission is hereby granted to any
 * person obtaining a copy of this software, associated documentation and/or
 * data (collectively the "Software"), free of charge and under any and all
 * copyright rights in the Software, and any and all patent rights owned or
 * freely licensable by each licensor hereunder covering either (i) the
 * unmodified Software as contributed to or provided by such licensor, or (ii)
 * the Larger Works (as defined below), to deal in both
 *
 * (a) the Software, and
 *
 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
 * one is included with the Software each a "Larger Work" to which the Software
 * is contributed by such licensors),
 *
 * without restriction, including without limitation the rights to copy, create
 * derivative works of, display, perform, and distribute the Software and make,
 * use, sell, offer for sale, import, export, have made, and have sold the
 * Software and the Larger Work(s), and to sublicense the foregoing rights on
 * either these or other terms.
 *
 * This license is subject to the following condition:
 *
 * The above copyright notice and either this complete permission notice or at a
 * minimum a reference to the UPL must be included in all copies or substantial
 * portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package com.oracle.truffle.api.utilities;

An utility value with three states, TRUE, FALSE, and UNDEFINED. TriState is preferable to using a Boolean value with Boolean.TRUE, Boolean.FALSE and null, because Boolean has a public constructor which requires the use of Boolean.equals(Object) to compare the values. The comparison with Boolean.equals(Object) is too slow. 
Since:
20.2/**
 * An utility value with three states, {@link #TRUE}, {@link #FALSE}, and {@link #UNDEFINED}.
 * {@link TriState} is preferable to using a {@link Boolean} value with {@link Boolean#TRUE},
 * {@link Boolean#FALSE} and <code>null</code>, because {@link Boolean} has a public constructor
 * which requires the use of {@link Boolean#equals(Object)} to compare the values. The comparison
 * with {@link Boolean#equals(Object)} is too slow.
 *
 * @since 20.2
 */
public enum TriState {

    
The state is true. Similar to Boolean.TRUE. 
Since:
20.2/**
     * The state is true. Similar to {@link Boolean#TRUE}.
     *
     * @since 20.2
     */
    TRUE,

    
The state is false. Similar to Boolean.FALSE. 
Since:
20.2/**
     * The state is false. Similar to {@link Boolean#FALSE}.
     *
     * @since 20.2
     */
    FALSE,

    
The state is undefined. Similar to null.
Since:
20.2/**
     * The state is undefined. Similar to <code>null</code>.
     *
     * @since 20.2
     */
    UNDEFINED;

    
Create a TriState from a primitive boolean. 
Since:
20.2/**
     * Create a {@link TriState} from a primitive boolean.
     *
     * @since 20.2
     */
    public static TriState valueOf(boolean b) {
        return b ? TRUE : FALSE;
    }

    
Create a TriState from a boxed Boolean explicitely checking for null and returning UNDEFINED. 
Since:
20.2/**
     * Create a {@link TriState} from a boxed {@link Boolean} explicitely checking for
     * <code>null</code> and returning {@link #UNDEFINED}.
     *
     * @since 20.2
     */
    public static TriState valueOf(Boolean b) {
        return b == null ? UNDEFINED : (Boolean.TRUE.equals(b) ? TRUE : FALSE);
    }

}