Suggestion: final struct initializers

[Q. Schroll]

On Friday, 4 December 2020 at 16:15:33 UTC, Mr T. wrote:
> On Friday, 4 December 2020 at 15:25:13 UTC, Jacob Carlborg 
> wrote:
>>
>> You can just use a constructor to achieve the same thing.
>
> Constructors need writing, these things exist automatically.

True, but if you really need it multiple times, a mixin template 
can serve you well: A quick and easy one is

     mixin template FinalCtor()
     {
         this(typeof(this.tupleof) args)
         {
             this.tupleof[] = args[];
         }
     }

but error messages if you forget arguments are rather bad. You 
could (in increasing value but also increasing difficulty)
(1) Add a templated @disable'd overload that catches all others 
and generates a @disabled error message.
(2) Add @disable'd overload that are one or more arguments short.
(3) Use https://dlang.org/phobos/std_traits.html#FieldNameTuple 
and other reflection to actually insert the member names. That 
way, you can use named arguments as soon as the corresponding DIP 
is implemented and best error messages. This solution is very 
convoluted using string mixins and from a maintenance viewpoint 
is worse than (2).

I've done (2) in https://run.dlang.io/is/vAGRMV
and (3) in https://run.dlang.io/is/PMT1PT