# bug #60850: Using (end+1) on non-existent variable assignment fails in Octave 6.2.0

 Submitted by: None Submitted on: Tue 29 Jun 2021 01:09:32 AM UTC Category: Interpreter Severity: 3 - Normal Priority: 5 - Normal Item Group: Matlab Compatibility Status: Wont Fix Assigned to: None Originator Name: Originator Email: -email is unavailable- Open/Closed: Closed Release: 6.2.0 Operating System: Any

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## Discussion

Sun 25 Jul 2021 08:05:28 PM UTC, comment #3:

Closing report as "won't fix".

Markus Mützel <mmuetzel>
Mon 05 Jul 2021 12:57:29 AM UTC, comment #2:

I agree with Rik.
The behavior now (version 6.2) is better and more reasonable than before (version 5.2).
Therefore, I think this is an improvement rather than a regression.

Anonymous
Tue 29 Jun 2021 03:58:47 PM UTC, comment #1:

The behavior of Octave now matches Matlab.  The special index 'end' is supposed to refer to the last element of an array.  If the array does not exist then one interpretation is that a last index can therefore not exist.  This is the position that Matlab takes and which Octave now implements.

A different interpretation would be that the 'end' index should always be valid.  But, it quickly gets complicated.  For example,

clear all
a(end) = 1
b(end+1) = 2

In the first case, 'end' must be set internally equal to 1 by the interpreter so that the variable 'a' is created with one element.

In the second case, should 'end' be equal to 0 or 1.  If it is equal to 0 then 'end+1' = 1 and the variable 'b' will have one element.  However, if 'end' is equal to 1 then the statement will be

b(1+1) = 2
b(2) = 2

and the variable 'b' will have two elements.

Rik <rik5>
Tue 29 Jun 2021 01:09:32 AM UTC, original submission:

In Octave 5.2.0 it works:

octave:1>  clear all
octave:2>  a(end+1) = 3
a =  3
octave:3>  a(end+1) = 5
a =

3   5

octave:4>  c{end+1} = 'abcd'
c =
{
[1,1] = abcd
}

octave:5>  c{end+1} = 1:5
c =
{
[1,1] = abcd
[1,2] =

1   2   3   4   5

}

But in Octave 6.2.0 it fails:

octave:1>  clear all
octave:2>  a(end+1) = 3
error: invalid use of 'end': may only be used to index existing value
octave:3>  c{end+1} = 'abcd'
error: invalid use of 'end': may only be used to index existing value

I'm not sure whether this is a "regression bug" or a "new feature" in Octave 6.2 ?

Anonymous

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• -email is unavailable- added by mmuetzel (Posted a comment)
• -email is unavailable- added by rik5 (Posted a comment)
• -email is unavailable- added by None (Submitted the item)
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