On 11/11/2011 01:42 PM, Steven Schveighoffer wrote:
> On Fri, 11 Nov 2011 16:10:12 -0500, Simon <s.d.hammett@gmail.com> wrote:
>
>> On 11/11/2011 19:04, Steven Schveighoffer wrote:
>>> On Fri, 11 Nov 2011 14:01:42 -0500, Steven Schveighoffer
>>> <schveiguy@yahoo.com> wrote:
>>>
>>>> There should be no bounds error in any case, an empty slice is valid.
>>>
>>> By "in any case" I meant in either debug or release mode.
>>>
>>> -Steve
>>
>> even when you index beyond the bounds of the slice?
>>
>> you may not actually be reading memory because it's zero length, but
>> it's still logically invalid; you've gone outside the valid range.
>
> You are not reading beyond the valid range. A zero-length slice is
> perfectly legal to point at the end of an array or other slice. Reading
> any data from a zero-length slice will cause an out-of-bounds error in
> debug mode, because it has no elements.
>
>> in vc9, if you increment an iterator beyond the valid range you get a
>> debug assert. that's caught quite a few bugs where I work when we
>> upgraded to vc9.
>
> I think you are misunderstanding what the $ actually means.
>
> It's the equivalent in C++ iterators to x.end.
>
> The pair of iterators x.end, x.end is a valid range. Going *beyond*
> x.end would be illegal. But iterating *to* x.end is legal (which would
> be the equivalent of [$..$] range), and you will not be able to convince
> me that vc9 doesn't allow it.
>
> -Steve

How about Jonathan's this comment: "It wouldn't surprise me if arr[500 .. 500] worked exactly the same way. Because the array is empty, it doesn't really matter  what values you gave it."

I think Simon is objecting to 500..500 being accepted (if at all). I agree that $..$ is correct.

Ali

Ali Çehreli Wrote:

> On 11/11/2011 01:42 PM, Steven Schveighoffer wrote:
> > On Fri, 11 Nov 2011 16:10:12 -0500, Simon <s.d.hammett@gmail.com> wrote:
> >
> >> On 11/11/2011 19:04, Steven Schveighoffer wrote:
> >>> On Fri, 11 Nov 2011 14:01:42 -0500, Steven Schveighoffer <schveiguy@yahoo.com> wrote:
> >>>
> >>>> There should be no bounds error in any case, an empty slice is valid.
> >>>
> >>> By "in any case" I meant in either debug or release mode.
> >>>
> >>> -Steve
> >>
> >> even when you index beyond the bounds of the slice?
> >>
> >> you may not actually be reading memory because it's zero length, but it's still logically invalid; you've gone outside the valid range.
> >
> > You are not reading beyond the valid range. A zero-length slice is perfectly legal to point at the end of an array or other slice. Reading any data from a zero-length slice will cause an out-of-bounds error in debug mode, because it has no elements.
> >
> >> in vc9, if you increment an iterator beyond the valid range you get a debug assert. that's caught quite a few bugs where I work when we upgraded to vc9.
> >
> > I think you are misunderstanding what the $ actually means.
> >
> > It's the equivalent in C++ iterators to x.end.
> >
> > The pair of iterators x.end, x.end is a valid range. Going *beyond* x.end would be illegal. But iterating *to* x.end is legal (which would be the equivalent of [$..$] range), and you will not be able to convince me that vc9 doesn't allow it.
> >
> > -Steve
> 
> How about Jonathan's this comment: "It wouldn't surprise me if arr[500 .. 500] worked exactly the same way. Because the array is empty, it doesn't really matter  what values you gave it."
> 
> I think Simon is objecting to 500..500 being accepted (if at all). I agree that $..$ is correct.
> 
> Ali

Oh my mistake!  I thought we were talking about arr[$..$]!

Yes, arr[500..500] would result in bounds errors if the array is only 7 elements. When I read it I thought it was just an arbitrary example to show another way to get an empty slice with an assumption that 500 is a valid index.

-Steve

On 11/11/2011 23:23, Steven Schveighoffer wrote:
> Ali Çehreli Wrote:
>
>> On 11/11/2011 01:42 PM, Steven Schveighoffer wrote:
>>> On Fri, 11 Nov 2011 16:10:12 -0500, Simon<s.d.hammett@gmail.com>  wrote:
>>>
>>>> On 11/11/2011 19:04, Steven Schveighoffer wrote:
>>>>> On Fri, 11 Nov 2011 14:01:42 -0500, Steven Schveighoffer
>>>>> <schveiguy@yahoo.com>  wrote:
>>>>>
>>>>>> There should be no bounds error in any case, an empty slice is valid.
>>>>>
>>>>> By "in any case" I meant in either debug or release mode.
>>>>>
>>>>> -Steve
>>>>
>>>> even when you index beyond the bounds of the slice?
>>>>
>>>> you may not actually be reading memory because it's zero length, but
>>>> it's still logically invalid; you've gone outside the valid range.
>>>
>>> You are not reading beyond the valid range. A zero-length slice is
>>> perfectly legal to point at the end of an array or other slice. Reading
>>> any data from a zero-length slice will cause an out-of-bounds error in
>>> debug mode, because it has no elements.
>>>
>>>> in vc9, if you increment an iterator beyond the valid range you get a
>>>> debug assert. that's caught quite a few bugs where I work when we
>>>> upgraded to vc9.
>>>
>>> I think you are misunderstanding what the $ actually means.
>>>
>>> It's the equivalent in C++ iterators to x.end.
>>>
>>> The pair of iterators x.end, x.end is a valid range. Going *beyond*
>>> x.end would be illegal. But iterating *to* x.end is legal (which would
>>> be the equivalent of [$..$] range), and you will not be able to convince
>>> me that vc9 doesn't allow it.
>>>
>>> -Steve
>>
>> How about Jonathan's this comment: "It wouldn't surprise me if arr[500
>> .. 500] worked exactly the same way. Because the array is empty, it
>> doesn't really matter  what values you gave it."
>>
>> I think Simon is objecting to 500..500 being accepted (if at all). I
>> agree that $..$ is correct.
>>
>> Ali
>
> Oh my mistake!  I thought we were talking about arr[$..$]!
>
> Yes, arr[500..500] would result in bounds errors if the array is only 7 elements. When I read it I thought it was just an arbitrary example to show another way to get an empty slice with an assumption that 500 is a valid index.
>
> -Steve

Yup, that was what I was on about. Should have been a bit clearer on that. Ta.

-- 
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