From @masak

<pmurias> I have found a rakudo bug
<pmurias> my $foo = [0,1,2,3,4];say $foo.elems;$foo[4] = Mu;$foo[3] =
Mu;say $foo.elems;$foo.delete(4);say $foo.elems;
<masak> r​: my $foo = [0,1,2,3,4];say $foo.elems;$foo[4] = Mu;$foo[3] =
Mu;say $foo.elems;$foo.delete(4);say $foo.elems
<+p6eval> rakudo 4fb07b​: OUTPUT«5␤5␤3␤»
* masak submits rakuodbug
<masak> pmurias++

From @masak

<tadzik> don't know about nqp, but on JVM we keep a constant value in
QRPA which says how many elements are there
<tadzik> it probably needs to be updated when we set Mu somewhere
<moritz> the problem is that if you delete an element that's not the
last, it set to Mu
<moritz> because we don't have an offchannel way to store an array
element as deleted
<pmurias> no
<moritz> no?
<tadzik> we have to settle of something​: do we count the number of
defined elements in the array, or do we count "the longest streak" of
elements?
<pmurias> the problem is that if you delete the last element all the
undefined elements before it get deletedf
<moritz> r​: my @​a = <a b c d>; @​a.delete(2); say @​a.perl
<p6eval> rakudo 4fb07b​: OUTPUT«Array.new("a", "b", Any, "d")␤»
<moritz> tadzik​: or do we simply keep the count separate, and don't do
any magic
<moritz> pmurias​: I'm (nearly) sure there's a spectest that requires
that
<pmurias> r​: class Foo {};my $foo = [0,1,2,3,4];say $foo.elems;$foo[4] =
Foo;$foo[3] = Foo;say $foo.elems;$foo.delete(4);say $foo.elems;
<p6eval> rakudo 4fb07b​: OUTPUT«5␤5␤3␤»
<pmurias> moritz​: it seems to be a bug in the code
<moritz> fwiw I agree that's undesirable
<moritz> but I can't quite imagine that it happened without any
intention
* masak adds this to the ticket
<pmurias> the spec seems to hold an distinction between elements that
aren't in an array and those that are set to an undefined value

@masak - Status changed from 'new' to 'open'

From @usev6

It looks like deleting the last element of an array no longer deletes the undefined elements before it​:

my $foo = [0,1,2,3,4]; say $foo.elems; say $foo.perl
5
[0, 1, 2, 3, 4]
$foo[4] = Any; $foo[3] = Any; say $foo.elems; say $foo.perl
5
[0, 1, 2, Any, Any]
$foo[4] :delete; say $foo.elems; say $foo.perl
4
[0, 1, 2, Any]

The same with class Foo​:

class Foo {}; my $foo = [0,1,2,3,4]; $foo[4] = Foo; $foo[3] = Foo; $foo[4] :delete; say $foo.elems; say $foo.perl
4
[0, 1, 2, Foo]

Is that the expected behaviour? The IRC log above expressed same doubts about that.

From @lizmat

On 08 Oct 2014, at 12​:30, Christian Bartolomaeus via RT <bugs-comment@​bugs6.perl.org> wrote​:

It looks like deleting the last element of an array no longer deletes the undefined elements before it​:

my $foo = [0,1,2,3,4]; say $foo.elems; say $foo.perl
5
[0, 1, 2, 3, 4]
$foo[4] = Any; $foo[3] = Any; say $foo.elems; say $foo.perl
5
[0, 1, 2, Any, Any]
$foo[4] :delete; say $foo.elems; say $foo.perl
4
[0, 1, 2, Any]

The same with class Foo​:

class Foo {}; my $foo = [0,1,2,3,4]; $foo[4] = Foo; $foo[3] = Foo; $foo[4] :delete; say $foo.elems; say $foo.perl
4
[0, 1, 2, Foo]

Is that the expected behaviour? The IRC log above expressed same doubts about that.

Setting an array element to Any, is *not* the same as deleting an entry. The proper way to do this is with the :delete adverb​:

$ 6 'my $a; $a[5]=1; say $a.elems; $a[5]​:delete; say $a.elems'
6
0

Liz

From @usev6

Well, this bug is gone, then. I added a test to S32-array/delete.t with the following commit​: Raku/roast@f386c96536

I had (and have) some difficulties to find the references in the spec for the correct behaviour -- especially with regard to the following quotes from an earlier IRC discussion. But that's not directly related to this bug and I'll bring it up on IRC.

<pmurias> the problem is that if you delete the last element all the undefined elements before it get deleted
[...]
<moritz> pmurias​: I'm (nearly) sure there's a spectest that requires that
[...]
<pmurias> the spec seems to hold an distinction between elements that aren't in an array and those that are set to an undefined value

@usev6 - Status changed from 'open' to 'resolved'