mixed-sign arithmetic and auto - c++

Andrei Alexandrescu (See Website For Email) wrote:
> James Dennett wrote:
>> Walter Bright wrote:
>>> James Dennett wrote:
>>>> Walter Bright wrote:
>>>>> Jerry Coffin wrote:
>>>>>> A design like you're advocating
>>>>>> that makes it easy for a bug to exist for years before it's even
>>>>>> noticed
>>>>>> almost inevitably _increases_ engineering costs by a huge margin.
>>>>>
>>>>> You're the first I've ever heard claim that undefined behavior reduces
>>>>> bugs, even by a "huge margin". I think it's an extraordinary claim.
>>>>
>>>> It's likely true.
>>>
>>> Sorry, I'm not buying it. How many bugs have you found in your code that
>>> were exposed by UB that would still have been bugs without UB?
>>
>> Hundreds, at a guess. Bugs that have been hidden when porting
>> between similar compilers/platforms but were exposed by others.
>> If the defined behavior had been that of the common platforms,
>> the bugs would have stayed hidden. Running tests across a wide
>> variety of platforms has brought to light many, many latent bugs.
>> As you yourself acknowledge, no test suite for a complex system
>> is complete; running it in different configurations across
>> platforms which have different behaviours helps to fill in some
>> of the gaps.
>
> Sorry, I'm not buying it either.

I'll sell harder.

> This is circular logic as it only works
> for a self-serving definition of a bug ("forgetting to code around an UB
> properly").

No it's not, as no, it doesn't

Unless you use useless definitions, and I prefer not to do so.

Defined integral sizes and wraparound behaviour can mask bugs.
Those bugs aren't just there because you need to "code around
an UB" -- they're there because you need to code so that your
code works, and respect limitations of finite arithmetic.

> I don't think it should be necessary to argue the bads of UB in this
> forum. It can only mean the discussion has meandered to a point where
> some fundamentals have been forgotten for the sake of the argument.

You might well be right.

> (I have some family friends who've had a son-in-law imprisoned. Our
> families got to talk about it during a party, and the man's
> mother-in-law said that he's doing great, he's in charge with the radio
> amd TV broadcast for the prison, he's getting good food, preferential
> visits, the works. She was very cheery about it all. It all sounded
> great, but my Dad put the finger on the issue. He said: "Wait a
> minute... she makes it sound like it's good to be in prison.")
>
> So wait a minute there. Undefined behavior is not good. We understand
> the necessity to tolerate it "for the greater good" (to quote a funny
> British movie), but it's not good.

Lack of definition is bad, but presence of a bad definition can
be even worse. The difficulty isn't in identifying "good" or
"bad" -- it's in determining "better" and "worse", and the
context in which the determination is valid.

But we're getting very meta here, and that usually fails on Usenet,
as in life.

-- James

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