/* * Copyright (c) 2010, 2013, 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. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * 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 jdk.nashorn.internal.runtime; import static jdk.nashorn.internal.lookup.Lookup.MH; import static jdk.nashorn.internal.runtime.ECMAErrors.typeError; import java.lang.invoke.MethodHandle; import java.lang.invoke.MethodHandles; import jdk.dynalink.CallSiteDescriptor; import jdk.dynalink.NamedOperation; import jdk.dynalink.StandardOperation; import jdk.dynalink.linker.GuardedInvocation; import jdk.dynalink.linker.support.Guards; import jdk.nashorn.internal.runtime.linker.NashornCallSiteDescriptor; /** * Unique instance of this class is used to represent JavaScript undefined. */ public final class Undefined extends DefaultPropertyAccess { private Undefined() { } private static final Undefined UNDEFINED = new Undefined(); private static final Undefined EMPTY = new Undefined(); // Guard used for indexed property access/set on the Undefined instance private static final MethodHandle UNDEFINED_GUARD = Guards.getIdentityGuard(UNDEFINED); /** * Get the value of {@code undefined}, this is represented as a global singleton * instance of this class. It can always be reference compared * * @return the undefined object */ public static Undefined getUndefined() { return UNDEFINED; } /** * Get the value of {@code empty}. This is represented as a global singleton * instanceof this class. It can always be reference compared. *
* We need empty to differentiate behavior in things like array iterators *
* @return the empty object
*/
public static Undefined getEmpty() {
return EMPTY;
}
/**
* Get the class name of Undefined
* @return "Undefined"
*/
@SuppressWarnings("static-method")
public String getClassName() {
return "Undefined";
}
@Override
public String toString() {
return "undefined";
}
/**
* Lookup the appropriate method for an invoke dynamic call.
* @param desc The invoke dynamic callsite descriptor.
* @return GuardedInvocation to be invoked at call site.
*/
public static GuardedInvocation lookup(final CallSiteDescriptor desc) {
final StandardOperation op = NashornCallSiteDescriptor.getFirstStandardOperation(desc);
if (op == null) {
return null;
}
switch (op) {
case CALL:
case NEW:
final String name = NashornCallSiteDescriptor.getOperand(desc);
final String msg = name != null? "not.a.function" : "cant.call.undefined";
throw typeError(msg, name);
case GET_PROPERTY:
case GET_ELEMENT:
case GET_METHOD:
// NOTE: we support GET_ELEMENT and SET_ELEMENT as JavaScript doesn't distinguish items from properties. Nashorn itself
// emits "GET_PROPERTY|GET_ELEMENT|GET_METHOD:identifier" for "