// example based on the MSDN Operator Overloading Sample (dbbool.cs)
public static void GenDbBool(AssemblyGen ag)
{
TypeGen DBBool = ag.Public.Struct("DBBool");
{
// Private field that stores -1, 0, 1 for dbFalse, dbNull, dbTrue:
FieldGen value = DBBool.Field <int>("value");
// Private constructor. The value parameter must be -1, 0, or 1:
CodeGen g = DBBool.Constructor().Parameter <int>("value");
{
g.Assign(value, g.Arg("value"));
}
// The three possible DBBool values:
FieldGen dbNull = DBBool.Public.Static.ReadOnly.Field(DBBool, "dbNull", Exp.New(DBBool, 0));
FieldGen dbFalse = DBBool.Public.Static.ReadOnly.Field(DBBool, "dbFalse", Exp.New(DBBool, -1));
FieldGen dbTrue = DBBool.Public.Static.ReadOnly.Field(DBBool, "dbTrue", Exp.New(DBBool, 1));
// Implicit conversion from bool to DBBool. Maps true to
// DBBool.dbTrue and false to DBBool.dbFalse:
g = DBBool.ImplicitConversionFrom <bool>("x");
{
Operand x = g.Arg("x");
g.Return(x.Conditional(dbTrue, dbFalse));
}
// Explicit conversion from DBBool to bool. Throws an
// exception if the given DBBool is dbNull, otherwise returns
// true or false:
g = DBBool.ExplicitConversionTo <bool>("x");
{
Operand x = g.Arg("x");
g.If(x.Field("value") == 0);
{
g.Throw(Exp.New(typeof(InvalidOperationException)));
}
g.End();
g.Return(x.Field("value") > 0);
}
// Equality operator. Returns dbNull if either operand is dbNull,
// otherwise returns dbTrue or dbFalse:
g = DBBool.Operator(Operator.Equality, DBBool, DBBool, "x", DBBool, "y");
{
Operand x = g.Arg("x"), y = g.Arg("y");
g.If(x.Field("value") == 0 || y.Field("value") == 0);
{
g.Return(dbNull);
}
g.End();
g.Return((x.Field("value") == y.Field("value")).Conditional(dbTrue, dbFalse));
}
// Inequality operator. Returns dbNull if either operand is
// dbNull, otherwise returns dbTrue or dbFalse:
g = DBBool.Operator(Operator.Inequality, DBBool, DBBool, "x", DBBool, "y");
{
Operand x = g.Arg("x"), y = g.Arg("y");
g.If(x.Field("value") == 0 || y.Field("value") == 0);
{
g.Return(dbNull);
}
g.End();
g.Return((x.Field("value") != y.Field("value")).Conditional(dbTrue, dbFalse));
}
// Logical negation operator. Returns dbTrue if the operand is
// dbFalse, dbNull if the operand is dbNull, or dbFalse if the
// operand is dbTrue:
g = DBBool.Operator(Operator.LogicalNot, DBBool, DBBool, "x");
{
Operand x = g.Arg("x");
g.Return(Exp.New(DBBool, -x.Field("value")));
}
// Logical AND operator. Returns dbFalse if either operand is
// dbFalse, dbNull if either operand is dbNull, otherwise dbTrue:
g = DBBool.Operator(Operator.And, DBBool, DBBool, "x", DBBool, "y");
{
Operand x = g.Arg("x"), y = g.Arg("y");
g.Return(Exp.New(DBBool, (x.Field("value") < y.Field("value")).Conditional(x.Field("value"), y.Field("value"))));
}
// Logical OR operator. Returns dbTrue if either operand is
// dbTrue, dbNull if either operand is dbNull, otherwise dbFalse:
g = DBBool.Operator(Operator.Or, DBBool, DBBool, "x", DBBool, "y");
{
Operand x = g.Arg("x"), y = g.Arg("y");
g.Return(Exp.New(DBBool, (x.Field("value") > y.Field("value")).Conditional(x.Field("value"), y.Field("value"))));
}
// Definitely true operator. Returns true if the operand is
// dbTrue, false otherwise:
g = DBBool.Operator(Operator.True, typeof(bool), DBBool, "x");
{
Operand x = g.Arg("x");
g.Return(x.Field("value") > 0);
}
// Definitely false operator. Returns true if the operand is
// dbFalse, false otherwise:
g = DBBool.Operator(Operator.False, typeof(bool), DBBool, "x");
{
Operand x = g.Arg("x");
g.Return(x.Field("value") < 0);
}
// Overload the conversion from DBBool to string:
g = DBBool.ImplicitConversionTo(typeof(string), "x");
{
Operand x = g.Arg("x");
g.Return((x.Field("value") > 0).Conditional("dbTrue",
(x.Field("value") < 0).Conditional("dbFalse",
"dbNull")));
}
// Override the Object.Equals(object o) method:
g = DBBool.Public.Override.Method <bool>("Equals").Parameter <object>("o");
{
g.Try();
{
g.Return((g.This() == g.Arg("o").Cast(DBBool)).Cast <bool>());
}
g.CatchAll();
{
g.Return(false);
}
g.End();
}
// Override the Object.GetHashCode() method:
g = DBBool.Public.Override.Method <int>("GetHashCode");
{
g.Return(value);
}
// Override the ToString method to convert DBBool to a string:
g = DBBool.Public.Override.Method <string>("ToString");
{
g.Switch(value);
{
g.Case(-1);
g.Return("DBBool.False");
g.Case(0);
g.Return("DBBool.Null");
g.Case(1);
g.Return("DBBool.True");
g.DefaultCase();
g.Throw(Exp.New <InvalidOperationException>());
}
g.End();
}
}
TypeGen Test = ag.Class("Test");
{
CodeGen g = Test.Static.Void("Main");
{
Operand a = g.Local(DBBool), b = g.Local(DBBool);
g.Assign(a, Static.Field(DBBool, "dbTrue"));
g.Assign(b, Static.Field(DBBool, "dbNull"));
g.WriteLine("!{0} = {1}", a, !a);
g.WriteLine("!{0} = {1}", b, !b);
g.WriteLine("{0} & {1} = {2}", a, b, a & b);
g.WriteLine("{0} | {1} = {2}", a, b, a | b);
// Invoke the true operator to determine the Boolean
// value of the DBBool variable:
g.If(b);
{
g.WriteLine("b is definitely true");
}
g.Else();
{
g.WriteLine("b is not definitely true");
}
g.End();
}
}
}