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package org.luaj.vm2;
/**
* Class to encapsulate behavior of the singleton instance {@code nil}
*
* There will be one instance of this class, {@link LuaValue#NIL},
* per Java virtual machine.
* However, the {@link Varargs} instance {@link LuaValue#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 LuaValue#isnil()}
* instead. By using that any ambiguities between
* {@link LuaValue#NIL} and {@link LuaValue#NONE} are avoided.
* @see LuaValue
* @see LuaValue#NIL
*/
public class LuaNil extends LuaValue {
static final LuaNil _NIL = new LuaNil();
public static LuaValue s_metatable;
LuaNil() {}
public int type() {
return LuaValue.TNIL;
}
public String toString() {
return "nil";
}
public String typename() {
return "nil";
}
public String tojstring() {
return "nil";
}
public LuaValue not() {
return LuaValue.TRUE;
}
public boolean toboolean() {
return false;
}
public boolean isnil() {
return true;
}
public LuaValue getmetatable() {
return s_metatable;
}
public boolean equals(Object o) {
return o instanceof LuaNil;
}
public LuaValue checknotnil() {
return argerror("value");
}
public boolean isvalidkey() {
return false;
}
// optional argument conversions - nil alwas falls badk to default value
public boolean optboolean(boolean defval) { return defval; }
public LuaClosure optclosure(LuaClosure defval) { return defval; }
public double optdouble(double defval) { return defval; }
public LuaFunction optfunction(LuaFunction defval) { return defval; }
public int optint(int defval) { return defval; }
public LuaInteger optinteger(LuaInteger defval) { return defval; }
public long optlong(long defval) { return defval; }
public LuaNumber optnumber(LuaNumber defval) { return defval; }
public LuaTable opttable(LuaTable defval) { return defval; }
public LuaThread optthread(LuaThread defval) { return defval; }
public String optjstring(String defval) { return defval; }
public LuaString optstring(LuaString defval) { return defval; }
public Object optuserdata(Object defval) { return defval; }
public Object optuserdata(Class c, Object defval) { return defval; }
public LuaValue optvalue(LuaValue defval) { return defval; }
}