"macro" expansion to build switch case code

[Steven Schveighoffer]

On 7/2/23 1:02 PM, Paul wrote:
> 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.

Use a static foreach:

```d
import std.traits; // for FieldNameTuple. there are other ways, but this 
is the most straightforward
switchlabel: // this is needed for break inside a static foreach
final switch(s) {
    static foreach(mem; FieldNameTuple!myS) {
      case mem ~ mem:
         __traits(getMember, this, mem) += n;
         break switchalbel;
    }
}
```

-Steve