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annotate graal/com.oracle.truffle.sl/src/com/oracle/truffle/sl/runtime/SLNull.java @ 21770:c76742cc2c6f

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Polishing inter-operability APIs: Exposing only Message, TruffleObject and ForeignAccess-related classes.
author Jaroslav Tulach <jaroslav.tulach@oracle.com>
date Mon, 08 Jun 2015 04:50:13 +0200
parents ed234a3178af
children
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1 /*
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2 * Copyright (c) 2012, 2014, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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4 *
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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5 * This code is free software; you can redistribute it and/or modify it
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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6 * under the terms of the GNU General Public License version 2 only, as
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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7 * published by the Free Software Foundation.
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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8 *
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
parents:
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12 * version 2 for more details (a copy is included in the LICENSE file that
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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13 * accompanied this code).
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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14 *
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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15 * You should have received a copy of the GNU General Public License version
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
parents:
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16 * 2 along with this work; if not, write to the Free Software Foundation,
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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18 *
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
71991b7a0f14 SL: Enhanced SimpleLanguage with support for if statements, function calls, function caching + inlining and builtins.
Christian Humer <christian.humer@gmail.com>
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20 * or visit www.oracle.com if you need additional information or have any
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Christian Humer <christian.humer@gmail.com>
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21 * questions.
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Christian Humer <christian.humer@gmail.com>
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22 */
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23 package com.oracle.truffle.sl.runtime;
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24
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25 import com.oracle.truffle.api.interop.ForeignAccess;
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26 import com.oracle.truffle.api.interop.TruffleObject;
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27
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28 /**
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29 * The SL type for a {@code null} (i.e., undefined) value. In Truffle, it is generally discouraged
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30 * to use the Java {@code null} value to represent the guest language {@code null} value. It is not
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31 * possible to specialize on Java {@code null} (since you cannot ask it for the Java class), and
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32 * there is always the danger of a spurious {@link NullPointerException}. Representing the guest
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33 * language {@code null} as a singleton, as in {@link #SINGLETON this class}, is the recommended
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34 * practice.
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35 */
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36 public final class SLNull implements TruffleObject {
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37
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38 /**
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39 * The canonical value to represent {@code null} in SL.
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40 */
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41 public static final SLNull SINGLETON = new SLNull();
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42
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Christian Wimmer <christian.wimmer@oracle.com>
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43 /**
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44 * Disallow instantiation from outside to ensure that the {@link #SINGLETON} is the only
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45 * instance.
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46 */
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Christian Humer <christian.humer@gmail.com>
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47 private SLNull() {
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48 }
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49
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50 /**
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51 * This method is, e.g., called when using the {@code null} value in a string concatenation. So
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52 * changing it has an effect on SL programs.
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53 */
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54 @Override
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55 public String toString() {
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56 return "null";
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57 }
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58
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59 @Override
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60 public ForeignAccess getForeignAccess() {
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61 return SLFunctionForeignAccess.INSTANCE;
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62 }
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63 }