Undefined.java revision 1782:fc972ab7d939 
1/*
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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
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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.
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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.dynalink.CallSiteDescriptor;
34import jdk.dynalink.NamedOperation;
35import jdk.dynalink.StandardOperation;
36import jdk.dynalink.linker.GuardedInvocation;
37import jdk.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        if (op == null) {
98            return null;
99        }
100        switch (op) {
101        case CALL:
102        case NEW:
103            final String name = NashornCallSiteDescriptor.getOperand(desc);
104            final String msg = name != null? "not.a.function" : "cant.call.undefined";
105            throw typeError(msg, name);
106        case GET_PROPERTY:
107        case GET_ELEMENT:
108        case GET_METHOD:
109            // NOTE: we support GET_ELEMENT and SET_ELEMENT as JavaScript doesn't distinguish items from properties. Nashorn itself
110            // emits "GET_PROPERTY|GET_ELEMENT|GET_METHOD:identifier" for "<expr>.<identifier>" and "GET_ELEMENT|GET_PROPERTY|GET_METHOD" for "<expr>[<expr>]", but we are
111            // more flexible here and dispatch not on operation name (getProp vs. getElem), but rather on whether the
112            // operation has an associated name or not.
113            if (!(desc.getOperation() instanceof NamedOperation)) {
114                return findGetIndexMethod(desc);
115            }
116            return findGetMethod(desc);
117        case SET_PROPERTY:
118        case SET_ELEMENT:
119            if (!(desc.getOperation() instanceof NamedOperation)) {
120                return findSetIndexMethod(desc);
121            }
122            return findSetMethod(desc);
123        default:
124        }
125        return null;
126    }
127
128    private static ECMAException lookupTypeError(final String msg, final CallSiteDescriptor desc) {
129        final String name = NashornCallSiteDescriptor.getOperand(desc);
130        return typeError(msg, name != null && !name.isEmpty()? name : null);
131    }
132
133    private static final MethodHandle GET_METHOD = findOwnMH("get", Object.class, Object.class);
134    private static final MethodHandle SET_METHOD = MH.insertArguments(findOwnMH("set", void.class, Object.class, Object.class, int.class), 3, NashornCallSiteDescriptor.CALLSITE_STRICT);
135
136    private static GuardedInvocation findGetMethod(final CallSiteDescriptor desc) {
137        return new GuardedInvocation(MH.insertArguments(GET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc);
138    }
139
140    private static GuardedInvocation findGetIndexMethod(final CallSiteDescriptor desc) {
141        return new GuardedInvocation(GET_METHOD, UNDEFINED_GUARD).asType(desc);
142    }
143
144    private static GuardedInvocation findSetMethod(final CallSiteDescriptor desc) {
145        return new GuardedInvocation(MH.insertArguments(SET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc);
146    }
147
148    private static GuardedInvocation findSetIndexMethod(final CallSiteDescriptor desc) {
149        return new GuardedInvocation(SET_METHOD, UNDEFINED_GUARD).asType(desc);
150    }
151
152    @Override
153    public Object get(final Object key) {
154        throw typeError("cant.read.property.of.undefined", ScriptRuntime.safeToString(key));
155    }
156
157    @Override
158    public void set(final Object key, final Object value, final int flags) {
159        throw typeError("cant.set.property.of.undefined", ScriptRuntime.safeToString(key));
160    }
161
162    @Override
163    public boolean delete(final Object key, final boolean strict) {
164        throw typeError("cant.delete.property.of.undefined", ScriptRuntime.safeToString(key));
165    }
166
167    @Override
168    public boolean has(final Object key) {
169        return false;
170    }
171
172    @Override
173    public boolean hasOwnProperty(final Object key) {
174        return false;
175    }
176
177    private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) {
178        return MH.findVirtual(MethodHandles.lookup(), Undefined.class, name, MH.type(rtype, types));
179    }
180}
181