Feature idea: .userinit property (or trait) to retrieve the initializer of a variable

[Maxim Fomin]

On Wednesday, 17 July 2013 at 11:28:18 UTC, Andrej Mitrovic wrote:
> I often need to re-initialize a variable back to its 
> user-defined
> initializer. For variables that have no user-defined 
> initializer, you
> can simply use .init. For fields of structs or classes you can
> actually use A.init.field, where A is the aggregate type. For 
> example:
>
> -----
> struct S
> {
>     int value = 5;
> }
>
> void main()
> {
>     S s;
>     s.value += 1;
>     s.value = S.init.value;
>     assert(s.value == 5);  // ok
> }
> -----
>
> But there's no equivalent for variables which do not belong to 
> any aggregate:
>
> -----
> void main()
> {
>     int value = 5;
>     value += 1;
>     // value = ??
>     assert(value == 5);
> }
> -----

I think this is not a fair comparison. Your S s could be S s = 
S(2) and you cannot retrieve S(2) just like in case with int 
value = 5. I see no difference between basic type variables and 
user-defined variables here.

Also, this reminds me replacing typedef by alias with loosing one 
nice feature - you could do typedef MyInt int = 5; but not with 
alias.

> One workaround is to factor out the initializer to a manifest
> constant, for example:

Other approach is to use UDA, it may be better then enum, but one 
still need extra typing. Having new trait seems to be a good idea 
but it needs to be figured out how it behaves in different 
contexts.