Mercurial > hg > truffle
view truffle/com.oracle.truffle.sl/src/com/oracle/truffle/sl/runtime/SLNull.java @ 22157:dc83cc1f94f2
Using fully qualified imports
author | Jaroslav Tulach <jaroslav.tulach@oracle.com> |
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date | Wed, 16 Sep 2015 11:33:22 +0200 |
parents | 31eb066d75ac |
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/* * Copyright (c) 2012, 2014, 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.sl.runtime; import com.oracle.truffle.api.interop.ForeignAccess; import com.oracle.truffle.api.interop.TruffleObject; /** * The SL type for a {@code null} (i.e., undefined) value. In Truffle, it is generally discouraged * to use the Java {@code null} value to represent the guest language {@code null} value. It is not * possible to specialize on Java {@code null} (since you cannot ask it for the Java class), and * there is always the danger of a spurious {@link NullPointerException}. Representing the guest * language {@code null} as a singleton, as in {@link #SINGLETON this class}, is the recommended * practice. */ public final class SLNull implements TruffleObject { /** * The canonical value to represent {@code null} in SL. */ public static final SLNull SINGLETON = new SLNull(); /** * Disallow instantiation from outside to ensure that the {@link #SINGLETON} is the only * instance. */ private SLNull() { } /** * This method is, e.g., called when using the {@code null} value in a string concatenation. So * changing it has an effect on SL programs. */ @Override public String toString() { return "null"; } @Override public ForeignAccess getForeignAccess() { return SLFunctionForeignAccess.create(); } }