The double conversion System::Variant::double returns a double or a reference to a double that is a conversion of this System::Variant::Variant. If the double* conversion is used, the System::Variant::double sets the varByRef bit, meaning that the System::Variant::Variant contains a reference as opposed to a value. 

If the conversion operation is not possible because of an invalid variant type conversion, an ESystem::Variant::VariantError exception is thrown.