I have the code:

	reduce!"a+b"(x)

where x is a int[] and I get an exception "Enforcement failed" at run time. This gives me enough information to say ¿que?

-- 
Russel. ============================================================================= Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder@ekiga.net 41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel@winder.org.uk London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder

On 09/30/2015 10:46 PM, Russel Winder via Digitalmars-d-learn wrote:
> I have the code:
>
> 	reduce!"a+b"(x)
>
> where x is a int[] and I get an exception "Enforcement failed" at run
> time. This gives me enough information to say ¿que?
>

It's coming from the following no-message enforce():

            enforce(!r.empty);


https://github.com/D-Programming-Language/phobos/blob/master/std/algorithm/iteration.d#L2481

You are using the no-seed version of reduce(), which uses the first element as seed, which means that the range cannot be empty.

Ali

On Wed, 2015-09-30 at 23:35 -0700, Ali Çehreli via Digitalmars-d-learn wrote:
> On 09/30/2015 10:46 PM, Russel Winder via Digitalmars-d-learn wrote:
> > I have the code:
> > 
> > 	reduce!"a+b"(x)
> > 
> > where x is a int[] and I get an exception "Enforcement failed" at
> > run
> > time. This gives me enough information to say ¿que?
> > 
> 
> It's coming from the following no-message enforce():
> 
>              enforce(!r.empty);
> 
> 
> https://github.com/D-Programming-Language/phobos/blob/master/std/algo
> rithm/iteration.d#L2481
> 
> You are using the no-seed version of reduce(), which uses the first element as seed, which means that the range cannot be empty.

Well that explanation (*) makes it abundantly clear that the error reporting from this part of Phobos is distinctly substandard, let alone below par.


(*) Which is clear and informative!
-- 
Russel. ============================================================================= Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder@ekiga.net 41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel@winder.org.uk London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder

On Thursday, 1 October 2015 at 07:08:00 UTC, Russel Winder wrote:
> On Wed, 2015-09-30 at 23:35 -0700, Ali Çehreli via Digitalmars-d-learn wrote:
>> On 09/30/2015 10:46 PM, Russel Winder via Digitalmars-d-learn wrote:
>> > [...]
>> 
>> It's coming from the following no-message enforce():
>> 
>>              enforce(!r.empty);
>> 
>> 
>> https://github.com/D-Programming-Language/phobos/blob/master/std/algo
>> rithm/iteration.d#L2481
>> 
>> You are using the no-seed version of reduce(), which uses the first element as seed, which means that the range cannot be empty.
>
> Well that explanation (*) makes it abundantly clear that the error reporting from this part of Phobos is distinctly substandard, let alone below par.
>
>
> (*) Which is clear and informative!

Bug report? Then it'll get fixed.

Am Thu, 01 Oct 2015 08:52:43 +0000
schrieb John Colvin <john.loughran.colvin@gmail.com>:

> On Thursday, 1 October 2015 at 07:08:00 UTC, Russel Winder wrote:
> > On Wed, 2015-09-30 at 23:35 -0700, Ali Çehreli via Digitalmars-d-learn wrote:
> >> On 09/30/2015 10:46 PM, Russel Winder via Digitalmars-d-learn wrote:
> >> > [...]
> >> 
> >> It's coming from the following no-message enforce():
> >> 
> >>              enforce(!r.empty);
> >> 
> >> 
> >> https://github.com/D-Programming-Language/phobos/blob/master/std/algo rithm/iteration.d#L2481
> >> 
> >> You are using the no-seed version of reduce(), which uses the first element as seed, which means that the range cannot be empty.
> >
> > Well that explanation (*) makes it abundantly clear that the error reporting from this part of Phobos is distinctly substandard, let alone below par.
> >
> >
> > (*) Which is clear and informative!
> 
> Bug report? Then it'll get fixed.

The problem is that in out minds addition has an implicit seed value of 0 and multiplication has 1, so a potentially empty range doesn't immediately raise a red flag.

The correct thing to use, following this train of thought, is http://dlang.org/phobos/std_algorithm_iteration.html#.sum (Additionally it provides better accuracy when summing up floating-point values.)

-- 
Marco

On Thu, 2015-10-01 at 08:52 +0000, John Colvin via Digitalmars-d-learn wrote:
> […]
> 
> Bug report? Then it'll get fixed.

https://issues.dlang.org/show_bug.cgi?id=15133

Timer running…  ;-)

-- 
Russel. ============================================================================= Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder@ekiga.net 41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel@winder.org.uk London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder