d-programming-language.org

[Steven Schveighoffer]

On Mon, 04 Jul 2011 16:16:04 -0400, eles <eles at eles.com> wrote:

>> Yes non-relase mode is slower, but we are probably talking
>> about a very significant slowdown here.  A lot of integer math
> happens in
>> D.
>
> What about testing only for user selected variables/types?

That's fine, just define a new type that does this, so it's user  
selected.  The ultimate goal is to define something like:

struct checkedInt { ... } // throws on overflows

debug(checkOverflows)
   alias _checkedInt cint;
else
   alias int cint; // default to no overflow checking

now you use cint anywhere you want to selectively enable overflow  
checking.  I don't know if the language is good enough to allow the  
definition of checkedInt to behave just like a builtin int.

>
>> I think a much more effective fix for the language would be to make
> slice
>> length a signed type.  Then you simply eliminate 99% of integer
> overflows
>> (it's very rare that a signed integer overflows, but not so
> unlikely that
>> an unsigned one does).
>
> I do not like that (Java-like) path too much. Why loosing half of
> length range?

I'm not saying it's the best solution, but it does solve a very common  
problem.  The largest issue with overflow is for unsigned types, because  
most integers are closer to zero than they are to their maximum,  
regardless of whether they are signed or not.  So having a signed integer  
protects against most cases of overflow -- when the integer goes less than  
zero.  Unless I'm solving coding puzzles, I rarely have cases where an  
integer exceeds its maximum.

Note that for 64-bit D, this effectively becomes a moot point -- a length  
of 2^63-1 is larger than any possible memory configuration you can  
currently have.

There is also the possibility of defining a large_array type which does  
use size_t for the length.

Anyway, this doesn't mean I think signed lengths are better than unsigned  
lengths.  It just means I think solving overflows using signed lengths is  
a better option than solving them using overflow detection and exception  
throwing.

-Steve