primitive value overflow

[luka8088]

Hello everyone.

Today I ran into a interesting issue. I wrote

   auto offset = text1.length - text2.length;

and in case text2 was longer then text1 I got something around 4294967291.

So I opened an issue:
http://d.puremagic.com/issues/show_bug.cgi?id=10093

I know that there is a perfectly valid reason for this behavior, and 
that this behavior is not undefined, but it is unexpected, especially 
because unsigned is never mentioned in the code. One solution that comes 
to mind is changing length to signed, but that makes no sense because 
length is never negative.

After some thinking a though came that maybe such value overflow should 
be treated the same way as array overflow and checked by druntime with 
optional disabling in production code (like array bound checks)?

I think it would be very helpful to get an error for such mistake (that 
could very easily happen by accident), and on the other hand it can be 
disabled (like all other checks).