How to implement this?

[Kenji Hara]

On Monday, 10 June 2013 at 09:42:56 UTC, Elvis wrote:
> class A
> {
>     enum TypeID = 1;
> }
> class B : A
> {
>     enum TypeID = 2;
> }
>
> class C : A
> {
>     enum TypeID = 3;
> }
>
> class D : B
> {
>     enum TypeID = 4;
> }
>
> ...
>
>
> Could anybody shed some light on how to make these TypeIDs auto 
> increment at compile time?

version(A)
{
     class A
     {
          enum TypeID = 1;
     }

     template IncrementTypeID(Class)
     {
         class IncrementTypeID : Class
         {
             enum TypeID = Class.TypeID + 1;
         }
     }
     alias B = IncrementTypeID!A;
     alias C = IncrementTypeID!B;
     alias D = IncrementTypeID!C;
}
version(B)  // more generative way
{
     template MakeContinuousClasses(int endID)
     {
         static if (endID > 0)
         {
             mixin MakeContinuousClasses!(endID - 1);

             enum className = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"[endID - 
1];
             static if (endID == 1)
                 enum baseClass = "";
             else
                 enum baseClass = " : " ~ 
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"[endID - 2];

             import std.conv : to;
             mixin("class "~className~baseClass~" { enum TypeID = 
"~endID.to!string~"; }");
         }
     }
     mixin MakeContinuousClasses!4;
}

// test case
import std.traits;
pragma(msg, A.TypeID, ", ", BaseClassesTuple!A);  // 1, (Object)
pragma(msg, B.TypeID, ", ", BaseClassesTuple!B);  // 2, (A, 
Object)
pragma(msg, C.TypeID, ", ", BaseClassesTuple!C);  // 3, (B, A, 
Object)
pragma(msg, D.TypeID, ", ", BaseClassesTuple!D);  // 4, (C, B, A, 
Object)

Kenji Hara