On Thu, Nov 17, 2022 at 10:16:04PM +0000, jwatson-CO-edu via
Digitalmars-d-learn wrote:
> On Thursday, 17 November 2022 at 21:05:43 UTC, H. S. Teoh wrote:
[...]
> > struct Atom {
> > F_Type kind;
> > union { // anonymous union
> > Atom* car; // ----------------- Left `Atom` Pointer
> > Atom* cdr; // ----------------- Right `Atom` Pointer
> > double num; // ----------------- Number value
> > string str; // ----------------- String value,
> > D-string underlies
> > bool bul; // ----------------- Boolean value
> > F_Error err = F_Error.NOVALUE; // Error code
> > }
> > }
[...]
> Thank you! This seems nice except there are a few fields that need to
> coexist.
> I need {`car`, `cdr`} -or- {`num`} -or- {`str`} -or- {`bul`}.
> `err` will be outside the union as well because I have decided that
> any type can have an error code attached. As in an error number
> (other than NaN) can be returned instead of reserving certain numbers
> to represent errors. Imagine if there was NaN for every datatype.
[...]
Just create a nested anonymous struct, like this:
struct Atom {
F_Type kind;
union { // anonymous union
struct {
Atom* car; // ----------------- Left `Atom`
Pointer
Atom* cdr; // ----------------- Right `Atom`
Pointer
}
struct {
double num; // ----------------- Number value
string str; // ----------------- String value,
D-string underlies
}
bool bul; // ----------------- Boolean value
}
F_Error err = F_Error.NOVALUE; // Error code
}
T
--
Meat: euphemism for dead animal. -- Flora
