[Issue 20030] Variant concat of char and string doesn't work

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20030

shove <shove at 163.com> changed:

           What    |Removed                     |Added
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                 CC|                            |shove at 163.com

--- Comment #1 from shove <shove at 163.com> ---
(In reply to Simen Kjaeraas from comment #0)
> The following code throws a VariantException complaining about different
> types (char and immutable(char)[]):
> 
> unittest {
>     import std.variant;
>     Variant v = "";
>     v ~= 'a';
> }
> 
> It's correct in some ways, but clearly a more useful behavior would be to
> concat the string and char and move on.

This shouldn't be a bug. Variant's design has strict restrictions on type
qualifiers, because string = immutable (char) [], so the ~ operator restricts
char. v ~= cast (immutable char)'a'; is possible because its qualifier is
consistent.

For these limitations, you can see the unittest:
https://github.com/dlang/phobos/blob/master/std/variant.d#L2655

There are many anomaly collection behaviors for qualifier inconsistencies.

I don't know whether it was intentionally designed to do this, or because it
was temporarily done for the sake of simplicity. I think, if there are no other
factors, it would be better to fix the variant implementation and remove these
restrictions.

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