Error demonstration

output

~/testing$ perl6 -v
This is Rakudo Star version 2017.10 built on MoarVM version 2017.10
implementing Perl 6.c.

~/testing$ perl6 -I . testit.p6 
Type check failed in assignment to $!list; expected Array[Str] but got Array[Str].new("this")
  in submethod BUILDALL at /home/ctilmes/testing/Testmod.pm6 (Testmod) line 1
  in block <unit> at testit.p6 line 4

testit.p6

use Testit;
use Testmod;

MyTestClass.new(list => Array[Str].new('this'));

Testit.pm6

class AnotherTestClass
{
    has Str @.something;
}

Testmod.pm6

class MyTestClass
{
    has Array[Str] $.list;
}