From zefram@fysh.org

Failure.new is a perfectly valid value that can be stored in a scalar
variable​:

$ ./perl6 -e 'my $a = Failure.new; say $a.WHICH'
Failure|60351944

But if used as the *default* value for a variable, it is not stored,
but is treated as an active indication of failure​:

$ ./perl6 -e 'my $a is default(Failure.new); say $a.WHICH'
===SORRY!=== Error while compiling -e
Failed
at -e​:1
Actually thrown at​:
  in any at src/Perl6/World.nqp​:2604
  in any ex-handle at src/Perl6/World.nqp​:3703
  in any apply_trait at src/Perl6/World.nqp​:2625
  in any at gen/moar/m-Perl6-Actions.nqp​:4467
  in any declare_variable at gen/moar/m-Perl6-Actions.nqp​:2682
  in any variable_declarator at gen/moar/m-Perl6-Actions.nqp​:2526
  in any variable_declarator at src/Perl6/Grammar.nqp​:2444
  in any declarator at src/Perl6/Grammar.nqp​:2310
  in any scoped at src/Perl6/Grammar.nqp​:2381
  in any scope_declarator​:sym<my> at ./blib/Perl6/Grammar.moarvm​:1
  in any scope_declarator at ./blib/Perl6/Grammar.moarvm​:1
  in any term​:sym<scope_declarator> at ./blib/Perl6/Grammar.moarvm​:1
  in any term at ./blib/Perl6/Grammar.moarvm​:1
  in any termish at src/Perl6/Grammar.nqp​:3641

This is not a case of the variable class rejecting the default value;
it's signalling the failure represented by the value. If the variable
is given a type constraint that the failure object doesn't satisfy,
then an error is correctly generated reporting that mismatch.

-zefram

From @jnthn

On Sun Sep 20 05​:14​:45 2015, zefram@​fysh.org wrote​:

Failure.new is a perfectly valid value that can be stored in a scalar
variable​:

$ ./perl6 -e 'my $a = Failure.new; say $a.WHICH'
Failure|60351944

But if used as the *default* value for a variable, it is not stored,
but is treated as an active indication of failure​:

$ ./perl6 -e 'my $a is default(Failure.new); say $a.WHICH'
===SORRY!=== Error while compiling -e
Failed
at -e​:1
Actually thrown at​:
in any at src/Perl6/World.nqp​:2604
in any ex-handle at src/Perl6/World.nqp​:3703
in any apply_trait at src/Perl6/World.nqp​:2625
in any at gen/moar/m-Perl6-Actions.nqp​:4467
in any declare_variable at gen/moar/m-Perl6-Actions.nqp​:2682
in any variable_declarator at gen/moar/m-Perl6-Actions.nqp​:2526
in any variable_declarator at src/Perl6/Grammar.nqp​:2444
in any declarator at src/Perl6/Grammar.nqp​:2310
in any scoped at src/Perl6/Grammar.nqp​:2381
in any scope_declarator​:sym<my> at ./blib/Perl6/Grammar.moarvm​:1
in any scope_declarator at ./blib/Perl6/Grammar.moarvm​:1
in any term​:sym<scope_declarator> at ./blib/Perl6/Grammar.moarvm​:1
in any term at ./blib/Perl6/Grammar.moarvm​:1
in any termish at src/Perl6/Grammar.nqp​:3641

This is not a case of the variable class rejecting the default value;
it's signalling the failure represented by the value. If the variable
is given a type constraint that the failure object doesn't satisfy,
then an error is correctly generated reporting that mismatch.

Fixed, and test added in S02-names/is_default.t.

The RT System itself - Status changed from 'new' to 'open'

@jnthn - Status changed from 'open' to 'resolved'