Make an enum idiomatic D - enhancing GNU Bison's Dlang support

[Adela Vais]

Hello,

I am working on GNU Bison, in order to enhance the current Dlang 
support.
The issue I have is regarding only D, there is no need to be 
familiar with Bison.

I need some advice on how to modify the current form of an enum, 
SymbolKind, to make it more idiomatic D (or leave it as it is - 
similar to how it is handled for the C++ support).

The problem is explained here [0]. (Java allows methods in enums 
[1].)

The way I modified it is by wrapping it in a struct and adding 
functionalities to change the already existing interaction with 
the enum as little as possible [2]. The code I changed in the 
repository is written in M4, so I will add the output after Bison 
is run:

   /* Symbol kinds.  */
   struct SymbolKind
   {
     public enum SymbolKindEnum
     {
     S_YYEMPTY = -2,  /* No symbol.  */
     S_YYEOF = 0,                   /* "end of file"  */
     S_YYerror = 1,                 /* error  */
     ...
     S_input = 14,                  /* input  */
     S_line = 15,                   /* line  */
     S_exp = 16,                    /* exp  */
     }

     private SymbolKindEnum yycode_;
     alias SymbolKindEnum this;

     this(int code)
     {
       yycode_ = cast(SymbolKindEnum) code;
     }

     public void opAssign(in SymbolKindEnum code)
     {
       yycode_ = code;
     }

     public bool opEquals(const int s)
     {
       return yycode_ == s;
     }

     SymbolKindEnum value() const
     {
       return yycode_;
     }

     /* YYTNAME[SYMBOL-NUM] -- String name of the symbol 
SYMBOL-NUM.
        First, the terminals, then, starting at \a YYNTOKENS_, 
nonterminals.  */
     private static string[] yytname_ = [
   "\"end of file\"", "error", "\"invalid token\"", "\"=\"", 
"\"+\"",
   "\"-\"", "\"*\"", "\"/\"", "\"(\"", "\")\"", "\"end of line\"",
   "\"number\"", "UNARY", "$accept", "input", "line", "exp", null
     ];

     public string toString() const
     {
       return yytname_[yycode_];
     }
   }

Should I modify it like this, or is it overkill? Is there a 
better way to deal with this?


[0]: https://github.com/akimd/bison/blob/master/TODO#L255
[1]: https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
[2]: https://github.com/adelavais/bison/tree/symbol-kind