Treating the abusive unsigned syndrome

[Andrei Alexandrescu]

(You may want to check your system's date, unless of course you traveled 
in time.)

Russell Lewis wrote:
> I'm of the opinion that we should make mixed-sign operations a 
> compile-time error.  I know that it would be annoying in some 
> situations, but IMHO it gives you clearer, more reliable code.

The problem is, it's much more annoying than one might imagine. Even 
array.length - 1 is up for scrutiny. Technically, even array.length + 1 
is a problem because 1 is really a signed int. We could provide 
exceptions for constants, but exceptions are generally not solving the 
core issue.

> IMHO, it's a mistake to have implicit casts that lose information.

Hear, hear.

> Want to hear a funny/sad, but somewhat related story?  I was chasing 
> down a segfault recently at work.  I hunted and hunted, and finally 
> found out that the pointer returned from malloc() was bad.  I figured 
> that I was overwriting the heap, right?  So I added tracing and 
> debugging everywhere...no luck.
> 
> I finally, in desperation, included <stdlib.h> to the source file (there 
> was a warning about malloc() not being prototyped)...and the segfaults 
> vanished!!!
> 
> The problem was that the xlc compiler, when it doesn't have the 
> prototype for a function, assumes that it returns int...but int is 32 
> bits.  Moreover, the compiler was happily implicitly casting that int to 
> a pointer...which was 64 bits.
> 
> The compiler was silently cropping the top 32 bits off my pointers.
> 
> And it all was a "feature" to make programming "easier."

Good story for reminding ourselves of the advantages of type safety!


Andrei