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* 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.
*
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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.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.
* <p>
* We need empty to differentiate behavior in things like array iterators
* <p>
* @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) {
switch (NashornCallSiteDescriptor.getStandardOperation(desc)) {
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:
// NOTE: we support GET:ELEMENT and SET:ELEMENT as JavaScript doesn't distinguish items from properties. Nashorn itself
// emits "GET:PROPERTY|ELEMENT|METHOD:identifier" for "<expr>.<identifier>" and "GET:ELEMENT|PROPERTY|METHOD" for "<expr>[<expr>]", but we are
// more flexible here and dispatch not on operation name (getProp vs. getElem), but rather on whether the
// operation has an associated name or not.
if (!(desc.getOperation() instanceof NamedOperation)) {
return findGetIndexMethod(desc);
}
return findGetMethod(desc);
case SET:
if (!(desc.getOperation() instanceof NamedOperation)) {
return findSetIndexMethod(desc);
}
return findSetMethod(desc);
default:
}
return null;
}
private static ECMAException lookupTypeError(final String msg, final CallSiteDescriptor desc) {
final String name = NashornCallSiteDescriptor.getOperand(desc);
return typeError(msg, name != null && !name.isEmpty()? name : null);
}
private static final MethodHandle GET_METHOD = findOwnMH("get", Object.class, Object.class);
private static final MethodHandle SET_METHOD = MH.insertArguments(findOwnMH("set", void.class, Object.class, Object.class, int.class), 3, NashornCallSiteDescriptor.CALLSITE_STRICT);
private static GuardedInvocation findGetMethod(final CallSiteDescriptor desc) {
return new GuardedInvocation(MH.insertArguments(GET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc);
}
private static GuardedInvocation findGetIndexMethod(final CallSiteDescriptor desc) {
return new GuardedInvocation(GET_METHOD, UNDEFINED_GUARD).asType(desc);
}
private static GuardedInvocation findSetMethod(final CallSiteDescriptor desc) {
return new GuardedInvocation(MH.insertArguments(SET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc);
}
private static GuardedInvocation findSetIndexMethod(final CallSiteDescriptor desc) {
return new GuardedInvocation(SET_METHOD, UNDEFINED_GUARD).asType(desc);
}
@Override
public Object get(final Object key) {
throw typeError("cant.read.property.of.undefined", ScriptRuntime.safeToString(key));
}
@Override
public void set(final Object key, final Object value, final int flags) {
throw typeError("cant.set.property.of.undefined", ScriptRuntime.safeToString(key));
}
@Override
public boolean delete(final Object key, final boolean strict) {
throw typeError("cant.delete.property.of.undefined", ScriptRuntime.safeToString(key));
}
@Override
public boolean has(final Object key) {
return false;
}
@Override
public boolean hasOwnProperty(final Object key) {
return false;
}
private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) {
return MH.findVirtual(MethodHandles.lookup(), Undefined.class, name, MH.type(rtype, types));
}
}