There does appear to be a bug, but I'd argue that it is in your code.
my %sum{Int} is default([]);
That line of code sets the default for all elements when they are first accessed
to the very same instance of an Array.
Remove the `is default([])`
To stop the warnings that would then happen you could use `andthen`
say (1..10).grep(-> $i { %sum{$i} andthen $_ == 2 });
Or you could use `.elems`
say (1..10).grep(-> $i { %sum{$i}.elems == 2 });
The way Moose in Perl 5 works around this is to give it a subroutine that will
produce the value to set it to then rather than a value. (slight simplification)
Basically Perl 6 dutifully did what you asked it to, and there currently
isn't as far as I know, a way to do what you intended.
So this isn't really a bug report, but a feature request.
The new feature may very well use the same syntax you have provided.
On Sun, Jun 18, 2017 at 4:52 PM, Michael Schaap
<perl6-bugs-follo...@perl.org> wrote:
> # New Ticket Created by Michael Schaap
> # Please include the string: [perl #131599]
> # in the subject line of all future correspondence about this issue.
> # <URL: https://rt.perl.org/Ticket/Display.html?id=131599 >
>
>
> #!/usr/bin/env perl6
>
> my %sum{Int} is default([]);
> %sum{4}.push: "1+3";
> %sum{4}.push: "2+2";
>
> say (1..10).grep(-> $i { %sum{$i} == 2 });
> # Expected output: (4)
> # Actual output: (1 2 3 4 5 6 7 8 9 10)
>
> %sum{3}.push: "1+2";
>
> say (1..10).grep(-> $i { %sum{$i} == 2 });
> # Expected output: (4)
> # Actual output: ()
>
> say %sum;
> # Expected output: {3 => [1+2], 4 => [1+3 2+2]}
> # Actual output: {}
>
> say %sum{4};
> # Expected output: [1+3 2+2]
> # Actual output: [1+3 2+2 1+2]
>
> # Without "is default([])" it works fine, except that the "grep" complains
> # (rightly) about uninitialized values.
>
> # % perl6 --version
> # This is Rakudo version 2017.04.3 built on MoarVM version
> 2017.04-53-g66c6dda
> # implementing Perl 6.c.
