How do I set a class member value by its name in a string?

[Mengu]

On Wednesday, 27 December 2017 at 20:54:17 UTC, bitwise wrote:
> On Wednesday, 27 December 2017 at 20:04:29 UTC, Marc wrote:
>> I'd like to set the members of a class by its name at runtime, 
>> I would do something like this:
>>
>>> __traits(getMember, myClass, name) = value;
>>
>> but since name is only know at runtime, I can't use 
>> __traits(). What's a workaround for this?
>
> I think you could write something using a combination of these 
> two things:
>
> https://dlang.org/phobos/std_traits.html#FieldNameTuple
> https://dlang.org/phobos/std_traits.html#Fields
>
> or maybe '.tupleof':
>
> https://dlang.org/spec/struct.html#struct_properties

there's also a simple workaround for fields with the same type: 
https://run.dlang.io/is/dsFajq

import std.stdio;

struct S {
   int x;
   int y;
}

auto setValue(ref S s, string field, int value) {
   foreach (fieldName; __traits(allMembers, S)) {
     if (fieldName == field) {
       __traits(getMember, s, fieldName) = value;
       break;
     }
   }
}

void main() {
   S s;
   s.setValue("x", 5);
   s.setValue("y", 25);
   writeln(s);
}


you can play with it to make it more generic. you can also create 
a mixin template that would generate setters for each field you 
would need a setter for and then in the run time you'd just be 
able to call them.