From q@cono.org.ua

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13​:22 < cono> rakudo​: class A​::B { has $.s = "hey" }; my $q = "B"; my
$l = gather { take "A​::$q".new; }; $l[0].s.say
13​:22 <+p6eval> rakudo 69561e​: OUTPUT«Null PMC access in get_repr()␤
in <anon> at line 22​:/tmp/kBN02ALah1␤ in
  'List​::at_pos' at line 1␤ in 'Any​::postcircumfix​:<[
]>' at line 1658​:CORE.setting␤ in main program body
  at line 1␤»
13​:22 < cono> Found how to reproduce ;)
13​:22 < moritz_> rakudo​: class A​::B { has $.s = "hey" }; my $q = "B";
my $l = gather { take "A​::$q".new; }; $l[0]
13​:23 <+p6eval> rakudo 69561e​: OUTPUT«Null PMC access in get_repr()␤
in <anon> at line 22​:/tmp/Brx41cXyGM␤ in
  'List​::at_pos' at line 1␤ in 'Any​::postcircumfix​:<[
]>' at line 1658​:CORE.setting␤ in main program body
  at line 1␤»
13​:23 < moritz_> rakudo​: class A​::B { has $.s = "hey" }; my $q = "B";
my $l = gather { take "A​::$q".new; };
13​:23 <+p6eval> rakudo 69561e​: ( no output )
13​:23 < moritz_> rakudo​: class A​::B { has $.s = "hey" }; my $q = "B";
my $l = gather { take "A​::$q".new; }; $l.eager
13​:23 <+p6eval> rakudo 69561e​: OUTPUT«Null PMC access in get_repr()␤
in <anon> at line 22​:/tmp/7avPB0sgCd␤ in main
  program body at line 1␤»
13​:24 < cono> moritz_​: it's only possible if prefix namespace present
A​::, without it, all good
13​:24 < cono> rakudo​: class B { has $.s = "hey" }; my $q = "B"; my $l
= gather { take "$q".new; }; $l[0].s.say
13​:24 <+p6eval> rakudo 69561e​: OUTPUT«hey␤»
13​:24 < gfldex> cono​: rakudobug@​perl.org

--
Varyanick I. Alex
icq​: 102 575 440
skype​: cono..
q@​cono.org.ua

From q@cono.org.ua

Simplest way to reproduce​:
% perl6 -e 'class A​::B { method hey { "hello world".say } }; "A​::B".new.hey'
Null PMC access in get_repr()
  in main program body at line 1

% perl6 -e 'class A { method hey { "hello world".say } }; "A".new.hey'
hello world

% perl6 -e 'class A​::B { method hey { "hello world".say } }; A​::B.new.hey'
hello world

Error happened only if :​: present in Str.

--
Varyanick I. Alex
icq​: 102 575 440
skype​: cono..
q@​cono.org.ua

From @moritz

FWIW Str.new should have never done a lookup by name, and it has stopped
doing it now. Use :​:($typeName) for dynamic lookup.

@moritz - Status changed from 'new' to 'resolved'