On Tuesday, 20 April 2021 at 19:56:33 UTC, Steven Schveighoffer
wrote:
I have had the need in some cases to *maybe* set a const value
inside a loop. One can sometimes abstract this into a lambda
function, but sometimes this is not possible (e.g. if the loop
is static). Not only that, but I may also want to keep
processing the loop and do something different if the value has
already been set instead of returning immediately, which
necessitates a second loop.
My use case is I have a property that is const inside a set of
types, and I want to verify that they all have the same value,
and extract what that value is.
I'm wondering if anyone has a "Write once" type, that is, a
type that allows you to write it exactly once, and is treated
like initialization on first setting (i.e. allows writing to
previously unused const data).
This type has to decide at runtime whether it has been set. So
it would kind of be like Nullable!T, but Nullable doesn't allow
setting when the T is const. Optional!T doesn't work either.
-Steve
Not quite your use case, I think, but std.typecons.Rebindable at
least allows you to bind a new const(object). Not write once
though.
I think I found that after a hint of its existence in
https://forum.dlang.org/thread/orpbvvjspibfpitnn...@forum.dlang.org
