nl.weeaboo.lua2.vm.LuaNil Maven / Gradle / Ivy

Go to download
/*******************************************************************************
 * Copyright (c) 2009-2011 Luaj.org. All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 ******************************************************************************/

package nl.weeaboo.lua2.vm;

import nl.weeaboo.lua2.LuaRunState;
import nl.weeaboo.lua2.io.IReadResolveSerializable;
import nl.weeaboo.lua2.io.LuaSerializable;

/**
 * Class to encapsulate behavior of the singleton instance {@code nil}
 * 
 * There will be one instance of this class, {@link LuaNil#NIL}, per Java virtual machine. However, the
 * {@link Varargs} instance {@link LuaConstants#NONE} which is the empty list, is also considered treated as a
 * nil value by default.
 * 
 * Although it is possible to test for nil using Java == operator, the recommended approach is to use the
 * method {@link #isnil()} instead. By using that any ambiguities between {@link LuaNil#NIL} and
 * {@link LuaConstants#NONE} are avoided.
 */
@LuaSerializable
public class LuaNil extends LuaValue implements IReadResolveSerializable {

    private static final long serialVersionUID = 1L;

    public static final LuaNil NIL = new LuaNil();

    LuaNil() {
    }

    @Override
    public Object readResolve() {
        // Special serialization returning the singleton
        return NIL;
    }

    @Override
    public int type() {
        return LuaConstants.TNIL;
    }

    @Override
    public String typename() {
        return "nil";
    }

    @Override
    public String tojstring() {
        return "nil";
    }

    @Override
    public LuaValue not() {
        return LuaBoolean.TRUE;
    }

    @Override
    public boolean toboolean() {
        return false;
    }

    @Override
    public boolean isnil() {
        return true;
    }

    @Override
    public boolean isvalidkey() {
        return false;
    }

    @Override
    public LuaValue getmetatable() {
        return LuaRunState.getCurrent().getMetatables().getNilMetatable();
    }

    @Override
    public int hashCode() {
        return 0;
    }

    @Override
    public boolean equals(Object o) {
        return o instanceof LuaNil;
    }

    @Override
    public LuaValue checknotnil() {
        throw argerror("value");
    }

    // optional argument conversions - nil always falls back to default value
    @Override
    public boolean optboolean(boolean defval) {
        return defval;
    }

    @Override
    public LuaClosure optclosure(LuaClosure defval) {
        return defval;
    }

    @Override
    public double optdouble(double defval) {
        return defval;
    }

    @Override
    public LuaFunction optfunction(LuaFunction defval) {
        return defval;
    }

    @Override
    public int optint(int defval) {
        return defval;
    }

    @Override
    public LuaInteger optinteger(LuaInteger defval) {
        return defval;
    }

    @Override
    public long optlong(long defval) {
        return defval;
    }

    @Override
    public LuaNumber optnumber(LuaNumber defval) {
        return defval;
    }

    @Override
    public LuaTable opttable(LuaTable defval) {
        return defval;
    }

    @Override
    public LuaThread optthread(LuaThread defval) {
        return defval;
    }

    @Override
    public String optjstring(String defval) {
        return defval;
    }

    @Override
    public LuaString optstring(LuaString defval) {
        return defval;
    }

    @Override
    public Object optuserdata(Object defval) {
        return defval;
    }

    @Override
    public  T optuserdata(Class c, T defval) {
        return defval;
    }

    @Override
    public LuaValue optvalue(LuaValue defval) {
        return defval;
    }

}