Re: [Liberty-eiffel] bug #44278

[Raphael Mack]

Hi Laurie,

first I have to apologize for (I) responding only now after 3 days (I
was on vacation) and (II) for not really responding since nearly one
year on your initial report - shame on us, and thanks for pushing this
up again.

I do not think this is a language problem but a library implementation
issue with the slice and subarray features. ISE defines subarray with a
return type "ARRAY[like item]", which is easy to implement basically as
we currently do it. With this return type it should work. This would
mean, that we'd have to remove the postcondition "same_dynamic_type" in
ARRAYED_COLLECTION.subarray.

The other option to solve this would be to implement ARRAY.slice as:
slice (min, max: INTEGER): like Current
   do
      Result := twin

      if max >= min then
         -- Slice not empty
         Result.remove_head(min - lower)
         Result.reindex(lower)
         Result.storage.slice_copy(0, storage, min - lower, max - lower)
      else
         Result.clear_count
      end
   end

With the benefit, that slice returns the same dynamic type, but with the
drawback of being quite slow, as the complete array is copied one
additional time.

To overcome this we could use standard_twin:
slice (min, max: INTEGER): like Current
   do
      Result := standard_twin
      Result.make(min, max)
         
      if max >= min then
         -- Slice not empty
         Result.reindex(lower)
         Result.storage.slice_copy(0, storage, min - lower, max - lower)
      else
         Result.clear_count
      end
   end

but in this case the behavior of slice is also not so nice, as it
doesn't copy the subclass instance of with its copy feature, so all
subclasses would additionally need to redefined slice to do the
necessary copying.

Currently my preference would be this last solution, but what do you
think?

@Laurie: would you like to try this with your old code, by just patching
the ARRAY-class in your adler installation?

Regards,
Rapha

Am Montag, den 28.12.2015, 19:01 +0000 schrieb Laurie Moye:
> Hi,
> 
> Last February, I submitted bug #22478. The problem was preventing me
> from recompiling some old code from SmallEiffel days. I went on to other
> things, but I would now like to get back to resurrecting this code.
> 
> Could someone please confirm that this is a bug, rather than some change
> in the language that I haven't understood?
> 
> The code where it originally occurred has a great tangle of
> inheritances, so I've reduced the example to something as simple as
> possible which displays the same (rather peculiar) error message. Have I
> reduced the code to something that wouldn't be expected to compile
> anyway? Would it be useful to make a longer example with code that
> actually does something sensible?
> 
> Best wishes,
>              Laurie
> 
>