Undefined.java revision 1483:7cb19fa78763
1/* 2 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26package jdk.nashorn.internal.runtime; 27 28import static jdk.nashorn.internal.lookup.Lookup.MH; 29import static jdk.nashorn.internal.runtime.ECMAErrors.typeError; 30 31import java.lang.invoke.MethodHandle; 32import java.lang.invoke.MethodHandles; 33import jdk.internal.dynalink.CallSiteDescriptor; 34import jdk.internal.dynalink.NamedOperation; 35import jdk.internal.dynalink.StandardOperation; 36import jdk.internal.dynalink.linker.GuardedInvocation; 37import jdk.internal.dynalink.linker.support.Guards; 38import jdk.nashorn.internal.runtime.linker.NashornCallSiteDescriptor; 39 40/** 41 * Unique instance of this class is used to represent JavaScript undefined. 42 */ 43public final class Undefined extends DefaultPropertyAccess { 44 45 private Undefined() { 46 } 47 48 private static final Undefined UNDEFINED = new Undefined(); 49 private static final Undefined EMPTY = new Undefined(); 50 51 // Guard used for indexed property access/set on the Undefined instance 52 private static final MethodHandle UNDEFINED_GUARD = Guards.getIdentityGuard(UNDEFINED); 53 54 /** 55 * Get the value of {@code undefined}, this is represented as a global singleton 56 * instance of this class. It can always be reference compared 57 * 58 * @return the undefined object 59 */ 60 public static Undefined getUndefined() { 61 return UNDEFINED; 62 } 63 64 /** 65 * Get the value of {@code empty}. This is represented as a global singleton 66 * instanceof this class. It can always be reference compared. 67 * <p> 68 * We need empty to differentiate behavior in things like array iterators 69 * <p> 70 * @return the empty object 71 */ 72 public static Undefined getEmpty() { 73 return EMPTY; 74 } 75 76 /** 77 * Get the class name of Undefined 78 * @return "Undefined" 79 */ 80 @SuppressWarnings("static-method") 81 public String getClassName() { 82 return "Undefined"; 83 } 84 85 @Override 86 public String toString() { 87 return "undefined"; 88 } 89 90 /** 91 * Lookup the appropriate method for an invoke dynamic call. 92 * @param desc The invoke dynamic callsite descriptor. 93 * @return GuardedInvocation to be invoked at call site. 94 */ 95 public static GuardedInvocation lookup(final CallSiteDescriptor desc) { 96 final StandardOperation op = NashornCallSiteDescriptor.getFirstStandardOperation(desc); 97 switch (op) { 98 case CALL: 99 case NEW: 100 final String name = NashornCallSiteDescriptor.getOperand(desc); 101 final String msg = name != null? "not.a.function" : "cant.call.undefined"; 102 throw typeError(msg, name); 103 case CALL_METHOD: 104 throw lookupTypeError("cant.read.property.of.undefined", desc); 105 case GET_PROPERTY: 106 case GET_ELEMENT: 107 case GET_METHOD: 108 // NOTE: we support GET_ELEMENT and SET_ELEMENT as JavaScript doesn't distinguish items from properties. Nashorn itself 109 // emits "GET_PROPERTY|GET_ELEMENT|GET_METHOD:identifier" for "<expr>.<identifier>" and "GET_ELEMENT|GET_PROPERTY|GET_METHOD" for "<expr>[<expr>]", but we are 110 // more flexible here and dispatch not on operation name (getProp vs. getElem), but rather on whether the 111 // operation has an associated name or not. 112 if (!(desc.getOperation() instanceof NamedOperation)) { 113 return findGetIndexMethod(desc); 114 } 115 return findGetMethod(desc); 116 case SET_PROPERTY: 117 case SET_ELEMENT: 118 if (!(desc.getOperation() instanceof NamedOperation)) { 119 return findSetIndexMethod(desc); 120 } 121 return findSetMethod(desc); 122 default: 123 } 124 return null; 125 } 126 127 private static ECMAException lookupTypeError(final String msg, final CallSiteDescriptor desc) { 128 final String name = NashornCallSiteDescriptor.getOperand(desc); 129 return typeError(msg, name != null && !name.isEmpty()? name : null); 130 } 131 132 private static final MethodHandle GET_METHOD = findOwnMH("get", Object.class, Object.class); 133 private static final MethodHandle SET_METHOD = MH.insertArguments(findOwnMH("set", void.class, Object.class, Object.class, int.class), 3, NashornCallSiteDescriptor.CALLSITE_STRICT); 134 135 private static GuardedInvocation findGetMethod(final CallSiteDescriptor desc) { 136 return new GuardedInvocation(MH.insertArguments(GET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc); 137 } 138 139 private static GuardedInvocation findGetIndexMethod(final CallSiteDescriptor desc) { 140 return new GuardedInvocation(GET_METHOD, UNDEFINED_GUARD).asType(desc); 141 } 142 143 private static GuardedInvocation findSetMethod(final CallSiteDescriptor desc) { 144 return new GuardedInvocation(MH.insertArguments(SET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc); 145 } 146 147 private static GuardedInvocation findSetIndexMethod(final CallSiteDescriptor desc) { 148 return new GuardedInvocation(SET_METHOD, UNDEFINED_GUARD).asType(desc); 149 } 150 151 @Override 152 public Object get(final Object key) { 153 throw typeError("cant.read.property.of.undefined", ScriptRuntime.safeToString(key)); 154 } 155 156 @Override 157 public void set(final Object key, final Object value, final int flags) { 158 throw typeError("cant.set.property.of.undefined", ScriptRuntime.safeToString(key)); 159 } 160 161 @Override 162 public boolean delete(final Object key, final boolean strict) { 163 throw typeError("cant.delete.property.of.undefined", ScriptRuntime.safeToString(key)); 164 } 165 166 @Override 167 public boolean has(final Object key) { 168 return false; 169 } 170 171 @Override 172 public boolean hasOwnProperty(final Object key) { 173 return false; 174 } 175 176 private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) { 177 return MH.findVirtual(MethodHandles.lookup(), Undefined.class, name, MH.type(rtype, types)); 178 } 179} 180