On Tue, Jun 12, 2018 at 12:55 PM, Joseph Brenner <doom...@gmail.com> wrote:
> Thanks, both your suggestion and JJ Merelo's work, but I think I like
> yours for readability:
>
> # # using binding, suggested by JJ Merelo <jjmer...@gmail.com>
> # my @y := @x but LookInside;
>
> # suggested by Elizabeth Mattijsen l...@dijkmat.nl
> my @y does LookInside = @x;
>
> I actually found the use of "but" in the objects docs to be
> tremendously confusing at first: it looks like some sort of
> conditional check, like "unless".
The reason `but` exists is basically for the following
my $v = 0 but True;
if $v { say $v } # prints 0
In Perl 5 it is common to return the string `"0 but true"` for a value that is
both 0 and true.
Since one of the design philosophies of Perl 6 is to reduce the number
of special cases this was made to be more generally useful.
Note that you should not do the following
my $v = 0;
$v does True;
say 'WTF!' if 0; # prints WTF!
Basically you can use `but` anywhere you like, but be careful with `does`.
> On Tue, Jun 12, 2018 at 1:01 AM, Elizabeth Mattijsen <l...@dijkmat.nl> wrote:
>>> On 12 Jun 2018, at 09:06, Joseph Brenner <doom...@gmail.com> wrote:
>>>
>>> I thought this would work to make a copy of @x but with the role
>>> "LookInside" attached to it:
>>>
>>> my @y = @x but LookInside;
>>>
>>> But that didn't add the role to @y. E.g.
That is effectively the same as:
my @y = (@x but LookInside).map: *.self;
That is @ sigiled variables tend to slurp in iterable values.
>>> say @y.^WHAT
If you want to print the name use `.^name`.
If you want the type object for more advanced usages use `.WHAT`.
>>>
>>> Would just report (Array), not (Array+{LookInside}).
>>
>> What you’re doing here, is assigning the elements of an Array but Lookinside
>> to a normal Array. The elements of the Array do not have any roles mixed
>> in, so you wind up with a normal Array with normal elements in them.
>> Perhaps you meant:
>>
>> my @y does LookInside = @x;
>>
>> Here you create an Array @y with the role LookInside mixed in, and *then*
>> assign the values from @x.
>>
