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.dynalink.CallSiteDescriptor;
34import jdk.dynalink.NamedOperation;
35import jdk.dynalink.linker.GuardedInvocation;
36import jdk.dynalink.linker.support.Guards;
37import jdk.nashorn.internal.runtime.linker.NashornCallSiteDescriptor;
38
39/**
40 * Unique instance of this class is used to represent JavaScript undefined.
41 */
42public final class Undefined extends DefaultPropertyAccess {
43
44    private Undefined() {
45    }
46
47    private static final Undefined UNDEFINED = new Undefined();
48    private static final Undefined EMPTY     = new Undefined();
49
50    // Guard used for indexed property access/set on the Undefined instance
51    private static final MethodHandle UNDEFINED_GUARD = Guards.getIdentityGuard(UNDEFINED);
52
53    /**
54     * Get the value of {@code undefined}, this is represented as a global singleton
55     * instance of this class. It can always be reference compared
56     *
57     * @return the undefined object
58     */
59    public static Undefined getUndefined() {
60        return UNDEFINED;
61    }
62
63    /**
64     * Get the value of {@code empty}. This is represented as a global singleton
65     * instanceof this class. It can always be reference compared.
66     * <p>
67     * We need empty to differentiate behavior in things like array iterators
68     * <p>
69     * @return the empty object
70     */
71    public static Undefined getEmpty() {
72        return EMPTY;
73    }
74
75    /**
76     * Get the class name of Undefined
77     * @return "Undefined"
78     */
79    @SuppressWarnings("static-method")
80    public String getClassName() {
81        return "Undefined";
82    }
83
84    @Override
85    public String toString() {
86        return "undefined";
87    }
88
89    /**
90     * Lookup the appropriate method for an invoke dynamic call.
91     * @param desc The invoke dynamic callsite descriptor.
92     * @return GuardedInvocation to be invoked at call site.
93     */
94    public static GuardedInvocation lookup(final CallSiteDescriptor desc) {
95        switch (NashornCallSiteDescriptor.getStandardOperation(desc)) {
96        case CALL:
97        case NEW:
98            final String name = NashornCallSiteDescriptor.getOperand(desc);
99            final String msg = name != null? "not.a.function" : "cant.call.undefined";
100            throw typeError(msg, name);
101        case GET:
102            // NOTE: we support GET:ELEMENT and SET:ELEMENT as JavaScript doesn't distinguish items from properties. Nashorn itself
103            // emits "GET:PROPERTY|ELEMENT|METHOD:identifier" for "<expr>.<identifier>" and "GET:ELEMENT|PROPERTY|METHOD" for "<expr>[<expr>]", but we are
104            // more flexible here and dispatch not on operation name (getProp vs. getElem), but rather on whether the
105            // operation has an associated name or not.
106            if (!(desc.getOperation() instanceof NamedOperation)) {
107                return findGetIndexMethod(desc);
108            }
109            return findGetMethod(desc);
110        case SET:
111            if (!(desc.getOperation() instanceof NamedOperation)) {
112                return findSetIndexMethod(desc);
113            }
114            return findSetMethod(desc);
115        default:
116        }
117        return null;
118    }
119
120    private static ECMAException lookupTypeError(final String msg, final CallSiteDescriptor desc) {
121        final String name = NashornCallSiteDescriptor.getOperand(desc);
122        return typeError(msg, name != null && !name.isEmpty()? name : null);
123    }
124
125    private static final MethodHandle GET_METHOD = findOwnMH("get", Object.class, Object.class);
126    private static final MethodHandle SET_METHOD = MH.insertArguments(findOwnMH("set", void.class, Object.class, Object.class, int.class), 3, NashornCallSiteDescriptor.CALLSITE_STRICT);
127
128    private static GuardedInvocation findGetMethod(final CallSiteDescriptor desc) {
129        return new GuardedInvocation(MH.insertArguments(GET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc);
130    }
131
132    private static GuardedInvocation findGetIndexMethod(final CallSiteDescriptor desc) {
133        return new GuardedInvocation(GET_METHOD, UNDEFINED_GUARD).asType(desc);
134    }
135
136    private static GuardedInvocation findSetMethod(final CallSiteDescriptor desc) {
137        return new GuardedInvocation(MH.insertArguments(SET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc);
138    }
139
140    private static GuardedInvocation findSetIndexMethod(final CallSiteDescriptor desc) {
141        return new GuardedInvocation(SET_METHOD, UNDEFINED_GUARD).asType(desc);
142    }
143
144    @Override
145    public Object get(final Object key) {
146        throw typeError("cant.read.property.of.undefined", ScriptRuntime.safeToString(key));
147    }
148
149    @Override
150    public void set(final Object key, final Object value, final int flags) {
151        throw typeError("cant.set.property.of.undefined", ScriptRuntime.safeToString(key));
152    }
153
154    @Override
155    public boolean delete(final Object key, final boolean strict) {
156        throw typeError("cant.delete.property.of.undefined", ScriptRuntime.safeToString(key));
157    }
158
159    @Override
160    public boolean has(final Object key) {
161        return false;
162    }
163
164    @Override
165    public boolean hasOwnProperty(final Object key) {
166        return false;
167    }
168
169    private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) {
170        return MH.findVirtual(MethodHandles.lookup(), Undefined.class, name, MH.type(rtype, types));
171    }
172}
173