int[7] arr = [1,2,3,4,5,6,7];
writeln(arr[$..$]);

this simply prints a newline... I expected a runtime error (or better a compile time error) but it does nothing ... why?

On Friday, November 11, 2011 11:46:02 RenatoL wrote:
> int[7] arr = [1,2,3,4,5,6,7];
> writeln(arr[$..$]);
> 
> this simply prints a newline... I expected a runtime error (or better a compile time error) but it does nothing ... why?

Probably because it's length is zero and therefore isn't actually a slice of the original array at all. 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.

- Jonathan M Davis

Yes, my fault. As Andrei write on his book

The situation m == n is acceptable and yields an empty slice

Thx.

On Fri, 11 Nov 2011 07:03:33 -0500, Jonathan M Davis <jmdavisProg@gmx.com> wrote:

> On Friday, November 11, 2011 11:46:02 RenatoL wrote:
>> int[7] arr = [1,2,3,4,5,6,7];
>> writeln(arr[$..$]);
>>
>> this simply prints a newline... I expected a runtime error (or better
>> a compile time error) but it does nothing ... why?
>
> Probably because it's length is zero and therefore isn't actually a slice of
> the original array at all. 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 would just make a minor correction that it *is* a slice of the original array.  It's just an empty slice.

BTW, I would have expected the output:

[]

(and testing, I see it does do this).

-Steve

"Jonathan M Davis" <jmdavisProg@gmx.com> wrote in message news:mailman.866.1321013026.24802.digitalmars-d-learn@puremagic.com...
> On Friday, November 11, 2011 11:46:02 RenatoL wrote:
>> int[7] arr = [1,2,3,4,5,6,7];
>> writeln(arr[$..$]);
>>
>> this simply prints a newline... I expected a runtime error (or better a compile time error) but it does nothing ... why?
>
> Probably because it's length is zero and therefore isn't actually a slice
> of
> the original array at all. 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.
>

Weird, I was certain that had given me bounds errors before, and so I've been careful to avoid doing it. Maybe that's changed since I last tried it.

On 11/11/2011 16:56, Nick Sabalausky wrote:
> "Jonathan M Davis"<jmdavisProg@gmx.com>  wrote in message
> news:mailman.866.1321013026.24802.digitalmars-d-learn@puremagic.com...
>> On Friday, November 11, 2011 11:46:02 RenatoL wrote:
>>> int[7] arr = [1,2,3,4,5,6,7];
>>> writeln(arr[$..$]);
>>>
>>> this simply prints a newline... I expected a runtime error (or better
>>> a compile time error) but it does nothing ... why?
>>
>> Probably because it's length is zero and therefore isn't actually a slice
>> of
>> the original array at all. 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.
>>
>
> Weird, I was certain that had given me bounds errors before, and so I've
> been careful to avoid doing it. Maybe that's changed since I last tried it.
>
>

You get bounds error in debug, but not release.
The bit about slices says you must not depend on bounds checking.

-- 
My enormous talent is exceeded only by my outrageous laziness.
http://www.ssTk.co.uk

On Fri, 11 Nov 2011 13:29:17 -0500, Simon <s.d.hammett@gmail.com> wrote:

> On 11/11/2011 16:56, Nick Sabalausky wrote:
>> "Jonathan M Davis"<jmdavisProg@gmx.com>  wrote in message
>> news:mailman.866.1321013026.24802.digitalmars-d-learn@puremagic.com...
>>> On Friday, November 11, 2011 11:46:02 RenatoL wrote:
>>>> int[7] arr = [1,2,3,4,5,6,7];
>>>> writeln(arr[$..$]);
>>>>
>>>> this simply prints a newline... I expected a runtime error (or better
>>>> a compile time error) but it does nothing ... why?
>>>
>>> Probably because it's length is zero and therefore isn't actually a slice
>>> of
>>> the original array at all. 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.
>>>
>>
>> Weird, I was certain that had given me bounds errors before, and so I've
>> been careful to avoid doing it. Maybe that's changed since I last tried it.
>>
>>
>
> You get bounds error in debug, but not release.
> The bit about slices says you must not depend on bounds checking.
>

There should be no bounds error in any case, an empty slice is valid.

-Steve

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

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.

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.

-- 
My enormous talent is exceeded only by my outrageous laziness.
http://www.ssTk.co.uk

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