Implementing Unary Operations
To allow the custom variant type to work with standard unary operators ( -, not), you must override the UnaryOp method.
UnaryOp has two parameters: the value of the operand and the operator. Implement this method to perform the operation and return the result using the same variable that contained the operand.
For example, the following
UnaryOp method comes from the
TComplexVariantType defined in the VarCmplx unit:
procedure TComplexVariantType.UnaryOp(var Right: TVarData; const Operator: TVarOp); begin if Right.VType = VarType then case Operator of opNegate: TComplexVarData(Right).VComplex.DoNegate; else RaiseInvalidOp; end else RaiseInvalidOp; end;
Note that for the logical not operator, which does not make sense for complex values, this method calls
RaiseInvalidOp to cause a runtime error.