Why there is too many uneccessary casts?

[H. S. Teoh]

On Tue, Jun 11, 2013 at 01:25:24PM -0400, Steven Schveighoffer wrote:
> On Tue, 11 Jun 2013 12:18:52 -0400, Adam D. Ruppe
> <destructionator at gmail.com> wrote:
> 
> >On Tuesday, 11 June 2013 at 16:05:30 UTC, Steven Schveighoffer wrote:
> >>CPU performs math at int level.
> >
> >eh, I wouldn't blame the hardware. You can do
> >
> >asm {
> >   mov AL, 10;
> >   add AL, 5;
> >}
> >
> >and it is allowed, it also don't spill into AH if you overflow it
> >(it just sets the carry flag). I'm sure it is different on
> >different processors, but x86 is pretty flexible.
> 
> Well, that is not what I knew, so good lesson :)
> 
> But I'd be surprised if the above was less costly than a full word
> addition.  I think that is the point of C's policy of integer
> promotion, which D adopts for the most part (although C allows it to
> go back into whatever).

It may or may not be less costly as full-word addition, but it
definitely allows the optimizer more wiggle room, because it allows more
byte-sized values to fit into registers before spilling over to memory
accesses.

But that doesn't really pertain to this discussion. :-P


> >>ubyte c = k;
> >>c += 1; // ok
> >>
> >>This I find extremely inconsistent...
> >
> >I'd be extremely annoyed if that required a cast. It's bleeding
> >obvious that you want it to assign back there....
> 
> I argue the consistency is both ways :)  I don't want to require a
> cast there (and in reality, where would the cast go?), but it seems
> that if you are doing math among bytes, or a byte and an integer
> that can fit into a byte, it should be quite obvious that you are
> working in the byte land.  The fact that
> 
> k += 1;
> 
> and
> 
> k = k + 1;
> 
> are treated differently is annoying.

Yeah, I agree that is annoyingly inconsistent. I'm sure there are good
reasons for it -- avoid common overflow bugs, for example, while not
making regular int arithmetic a pain to work with by requiring casts
everywhere. But still, it *is* an inconsistency, and it's still
annoying.


T

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Ruby is essentially Perl minus Wall.