Need Advice: Union or Variant?

[jwatson-CO-edu]

On Saturday, 19 November 2022 at 03:38:26 UTC, jwatson-CO-edu 
wrote:
> Thank you, something similar to what you suggested reduced the 
> atom size from 72 bytes to 40.

Oh, based on another forum post I added constructors in addition 
to reducing the atom size 44%.

```d
struct Atom{
     F_Type  kind; // What kind of atom this is
     union{
         double  num; // NMBR: Number value
         string  str; // STRN: String value, D-string
         bool    bul; // BOOL: Boolean value
         struct{ // ---- CONS: pair
             Atom* car; // Left  `Atom` Pointer
             Atom* cdr; // Right `Atom` Pointer
         }
         struct{ // ---- EROR: Code + Message
             F_Error err; // Error code
             string  msg; // Detailed desc
         }
     }
     // https://forum.dlang.org/post/omsbr8$7do$1@digitalmars.com
     this( double n ){ kind = F_Type.NMBR; num = n; } // make 
number
     this( string s ){ kind = F_Type.STRN; str = s; } // make 
string
     this( bool   b ){ kind = F_Type.BOOL; bul = b; } // make bool
     this( Atom* a, Atom* d ){ kind = F_Type.CONS; car = a; cdr = 
d; } // make cons
     this( F_Error e, string m ){ kind = F_Type.EROR; err = e; msg 
= m; } // make error
}
```