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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.
/** * 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 undefined, this is represented as a global singleton instance of this class. It can always be reference compared
Returns:the undefined object
/** * 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 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

Returns:the empty object
/** * 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
Returns:"Undefined"
/** * 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.
Params:
  • desc – The invoke dynamic callsite descriptor.
Returns:GuardedInvocation to be invoked at call site.
/** * 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); case REMOVE: if (!(desc.getOperation() instanceof NamedOperation)) { return findDeleteIndexMethod(desc); } return findDeleteMethod(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 final MethodHandle DELETE_METHOD = MH.insertArguments(findOwnMH("delete", boolean.class, Object.class, boolean.class), 2, false); 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); } private static GuardedInvocation findDeleteMethod(final CallSiteDescriptor desc) { return new GuardedInvocation(MH.insertArguments(DELETE_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc); } private static GuardedInvocation findDeleteIndexMethod(final CallSiteDescriptor desc) { return new GuardedInvocation(DELETE_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)); } }