What is the "right" way to create a generic type getter (and setter) ?

[Cym13]

On Thursday, 15 March 2018 at 15:48:52 UTC, James Blachly wrote:
> On Wednesday, 14 March 2018 at 22:58:25 UTC, ag0aep6g wrote:
>> You can probably get around the (manually maintained?) 
>> `FIELDS` array with `.tupleof` or something similar:
>>
>> ----
>> static foreach (i, f; S.tupleof)
>> {
>>     case __traits(identifier, f):
>> }
>> ----
>>
>>> Any pointers / design patterns on this particular type of 
>>> problem class would be greatly appreciated.  (Sidenote, I 
>>> realize I could probably use the witchcraft library, but I am 
>>> also using this as exercise to learn D beyond the basics).
>>
>> You simply cannot have a method that returns different types 
>> based on a run-time value. You could possibly return a 
>> std.variant.Variant. But if the goal is just to print the 
>> value to the screen, all you need is a string.
>>
>> So the signature would be `string get(string field)`. And for 
>> the implementation you could use `.tupleof` to iterate over 
>> all fields, and then return `f.to!string`.
>>
>> `set` can be done similarly. Take two `string`s: the field 
>> name, and the value. `static foreach` over all fields. On a 
>> match, convert the given value string to the type of the field 
>> that matched.
>
> Thanks - to!string certainly seems to be a good option in this 
> case (CLI) and I was definitely overthinking this part, perhaps 
> because I was trying to write everything as generically / 
> extensibly as possible (for example, to use the same framework 
> but with a GUI or web front end, for example).
>
> I would still think an AA mapping (string) field name to a type 
> would be useful and will see if I can construct it as a mixin 
> using typeof(Struct.member) somehow.

If you're comming from python you may appreciate that you don't 
need getter/setters in D either. Just as you have @property in 
python which allows you to change at any time from a simple 
attribute to a method (be it reading or writing) you have a 
property syntax in D:

     struct S {
         int a;

         int _b;

         auto b() {
             return _b;
         }

         void b(int val) {
             _b = val;
         }
     }


     void main(string[] args) {
         S s;
         s.a = 24;
         writeln(s.a);

         s.b = 42;
         writeln(s.b);
     }