Bug or logic error in if with auto?

[Nick Treleaven]

On 03/12/2012 14:22, Nick Treleaven wrote:
> Most programmers would probably just pollute the existing scope:
>
> auto x = "thing" in arr;
> if (x && *x == 45)
> {
>      ...
> }
>
> I expect this is because wrapping the above in {} for a new scope is
> just too ugly, introducing more nesting and indentation.
>
> It would be nice if there was a way of introducing a new scope just for
> a declaration and the next statement, something like:
>
> with auto x = "thing" in arr:
> if (x && *x == 45)
> {
>      // x is still visible here
> }
>
> That would overload 'with' with a different meaning, but would be clear
> enough IMO. It would be useful with other constructs like while, do,
> foreach, etc. I think it would be more elegant than allowing a
> declaration clause in all constructs (like the 'for' statement has).

The above syntax was inspired from Tove and Tommi's existing solution (I 
couldn't find the link earlier):
http://forum.dlang.org/post/nyhpuaoxkeunwqongfyk@forum.dlang.org

The idea was to use a Tuple to wrap the new variable:

with (Tuple!(int, "a")(getInt()))
if (a > 9)
     ...

I've now improved on this syntax using opDispatch and opAssign so we can 
write:

with (wrap.a = getInt())
if (a > 9)
     ...

Whether using this in real code is good practice or not may be debatable ;-)

Code:
http://dpaste.dzfl.pl/4dbefd84