Perhaps also worth noting that this applies to other holes as well, e.g. those
created by extending an array:
my @a = 42; @a[5] = 49; say |@a # 42(Mu)(Mu)(Mu)(Mu)49
In fact, this the actual problem the user had.
On 2017-07-22 18:52:03, c...@zoffix.com wrote:
> On Sat, 22 Jul 2017 18:48:38 -0700, c...@zoffix.com wrote:
> > The current behaviour kinda makes sense when you squint at it, but
> > today we had a user[^1]who was surprised by it, so I'm filing it as a
> > ticket, if maybe there's some Better Way this can be done with.
> >
> > When you :delete an element from the Array, you get nqp::null stuffed
> > into the position, which gets converted to `is default` value when
> > you
> > look it up again:
> >
> > <Zoffix__> m: use nqp; my @a is default(42) = <a b c>; @a[1]:delete;
> > dd @a
> > <camelia> rakudo-moar b14721: OUTPUT: «Array @a = ["a", 42, "c"]»
> >
> > However, if you now convert that Array to a Slip or a List, the hole
> > is left as a bare Mu and doesn't get turned into a default value,
> > which is lost:
> >
> > <Zoffix__> m: use nqp; my @a is default(42) = <a b c>; @a[1]:delete;
> > dd @a.Slip
> > <camelia> rakudo-moar b14721: OUTPUT: «slip("a", Mu, "c")»
> >
> > <Zoffix__> m: use nqp; my @a is default(42) = <a b c>; @a[1]:delete;
> > dd @a.List
> > <camelia> rakudo-moar b14721: OUTPUT: «("a", Mu, "c")»
> >
> > So it makes sense that without `is default` you don't get an `is
> > default` value, but at the same time, Mu is not a great value to deal
> > with...
> >
> > [1] https://irclog.perlgeek.de/perl6/2017-07-22#i_14908846
>
>
> And actually both .flat and .Seq do get `is default` value instead of
> Mu, so at the very least there's some inconsistency here:
>
> <Zoffix__> m: use nqp; my @a is default(42) = <a b c>; @a[1]:delete;
> dd @a.flat
> <camelia> rakudo-moar b14721: OUTPUT: «("a", 42, "c").Seq»
> <Zoffix__> m: use nqp; my @a is default(42) = <a b c>; @a[1]:delete;
> dd @a.Seq
> <camelia> rakudo-moar b14721: OUTPUT: «("a", 42, "c").Seq»
