From zefram@fysh.org

(Nil,).perl
(Nil,)
(Nil,).Array.perl
[Any]

The coercion from List to Array transforms the Nil element value into
an Any. This is a poor coercion. It is perfectly possible for an Array
to contain an element of Nil value, so the coercion ought to preserve
that value.

-zefram

From @lizmat

On 9 Mar 2017, at 12​:57, Zefram (via RT) <perl6-bugs-followup@​perl.org> wrote​:

# New Ticket Created by Zefram
# Please include the string​: [perl #​130962]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl6/Ticket/Display.html?id=130962 >

(Nil,).perl
(Nil,)
(Nil,).Array.perl
[Any]

The coercion from List to Array transforms the Nil element value into
an Any. This is a poor coercion. It is perfectly possible for an Array
to contain an element of Nil value, so the coercion ought to preserve
that value.

$ 6 'my @​a = Nil; dd @​a'
Array @​a = [Any]

$ 6 'my @​a = (Nil,); dd @​a’ # more direct translation
Array @​a = [Any]

$ 6 'dd my @​ = (Nil,)'
Array @​ = [Any]

In all of these cases, Nil becomes Any after coercion.

The *only* way to keep Nil in here, is to make it the default​:

$ 6 'dd my @​ is default(Nil) = (Nil,)'
Array @​ = [Nil]

I’m not sure we want to do that for all Array coercions, or for all Array creation for that matter (seeing RT #​130963).

The RT System itself - Status changed from 'new' to 'open'

From zefram@fysh.org

Elizabeth Mattijsen via RT wrote​:

The *only* way to keep Nil in here, is to make it the default​:

There's also binding​:

my @​a; @​a[0] := Nil
Nil
@​a[0]
Nil

I'm not sure we want to do that for all Array coercions,

It's not required for all Array coercions. Only where there's a Nil
element value.

or for all Array creation for that matter (seeing RT #​130963).

That one's even more open. Although it's rather surprising behaviour
for the [] Array constructor to mangle Nil (since it doesn't overtly
involve assignment), I didn't commit to that being the part with the bug.
If you'd prefer for [] to keep the Nil manglement, it's open to Array.perl
to emit more complex code that doesn't just feed the Nil to [].

-zefram