"macro" expansion to build switch case code

[Paul]

I have a struct similar to the following example.  I'd like to 
build an adder method without having to code the whole method.  
How do I use the D language to do this?  Template, mixins, 
CTFE..all of them?

```d
struct myS {
     int a, b, c, d, e, f, g, h, i;
     adder(string s, int n) {
         final switch (s) {
             case "aa" :
                 a += n; break;
             case "bb" :
                 b += n; break;
            ...
```
Thanks for any assistance.