Mercurial > hg > graal-compiler
view graal/com.oracle.truffle.sl/src/com/oracle/truffle/sl/runtime/SLNull.java @ 14155:1ac6195ee586
mx: use os.sep
author | Bernhard Urban <bernhard.urban@jku.at> |
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date | Wed, 12 Mar 2014 11:45:15 +0100 |
parents | b16ec83edc73 |
children | 1d3c23e675ed |
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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. * * 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. * * 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 * or visit www.oracle.com if you need additional information or have any * questions. */ package com.oracle.truffle.sl.runtime; /** * 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 { /** * 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"; } }