Substring by range parameter (bug?)

ruby-talk
1

for ranges, start must be <= end and -1 is not <= -2

eg. for the string "foobar":

    ---- --- ----
    char idx nidx
    ---- --- ----
    f 0 -6
    o 1 -5
    o 2 -4
    b 3 -3
    a 4 -2
    r 5 -1

  ~ > irb
  irb(main):001:0> "foobar"[-2..-1]
  => "ar"
  irb(main):002:0> "foobar"[-6..-4]
  => "foo"
  irb(main):003:0> "foobar"[-3..-1]
  => "bar"

cheers.

Thanks. I know that.
That is why I expect "foobar"[-1..-2] returns nil as "foobar"[-1..-3] did.
But it returns an empty string instead of nil, it seems to me that this is a bug.
In fact, if start is -n and end is < -(n+1), it will return nil. ( like -2..-4, -2..-5 )
The problem is only when start is -n and end is -(n+1), it always return empty string. (like -2..-3, -3..-4)
How does it possible that a substring is empty string ?
And the tricky part is, it do existe and you can re-assign to it too. like:
s = "foobar"; s[-3..-4] = "xxx";
So, my question is, is this a bug, or special feature for substring when range is -n..-(n+1) ?

···

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2

for ranges, start must be <= end and -1 is not <= -2

eg. for the string "foobar":

    ---- --- ----
    char idx nidx
    ---- --- ----
    f 0 -6
    o 1 -5
    o 2 -4
    b 3 -3
    a 4 -2
    r 5 -1

  ~ > irb
  irb(main):001:0> "foobar"[-2..-1]
  => "ar"
  irb(main):002:0> "foobar"[-6..-4]
  => "foo"
  irb(main):003:0> "foobar"[-3..-1]
  => "bar"

cheers.

Thanks. I know that.

sorry - did not read your post closely enough.

That is why I expect "foobar"[-1..-2] returns nil as "foobar"[-1..-3] did.
But it returns an empty string instead of nil, it seems to me that this is a
bug.

hmmmm. does seem strange.

In fact, if start is -n and end is < -(n+1), it will return nil. ( like
-2..-4, -2..-5 )
The problem is only when start is -n and end is -(n+1), it always return
empty string. (like -2..-3, -3..-4)

strange.

How does it possible that a substring is empty string ?

well, there is always

   idx = 0
   len = 0
   'foobar'[idx, len]

And the tricky part is, it do existe and you can re-assign to it too. like:
s = "foobar"; s[-3..-4] = "xxx";
So, my question is, is this a bug, or special feature for substring when
range is -n..-(n+1) ?

i can only imagine it happen somehow because

   len = end - start_inclusive + 1

so

   0 = (-4 - -3) + 1

and 0 len give back empty string... kind of looks like it from the source:

   static VALUE
   rb_str_aref(str, indx)
       VALUE str;
       VALUE indx;
   {
       long idx;

       switch (TYPE(indx)) {

<snip>

         default:
           /* check if indx is Range */
           {
               long beg, len;
               switch (rb_range_beg_len(indx, &beg, &len, RSTRING(str)->len, 0)) {
                 case Qfalse:
                   break;
                 case Qnil:
                   return Qnil;
                 default:
                   return rb_str_substr(str, beg, len);
               }
           }
           idx = NUM2LONG(indx);
           goto num_index;
       }
       return Qnil; /* not reached */
   }

i've looked at rb_range_beg_len and this looks to be the problem - but how to
fix it? should these types of ranges throw an error in the first place? like

-1...-1

??

-a

···

On Thu, 22 Jul 2004, D T wrote:
--

EMAIL :: Ara [dot] T [dot] Howard [at] noaa [dot] gov
PHONE :: 303.497.6469
A flower falls, even though we love it;
and a weed grows, even though we do not love it. --Dogen

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