Nowadays the error message is:
$ perl6 -e 'subset UInt of Int where * >= 0; sub foo (UInt $bar?) { }; foo()'
Invocant requires an instance of type Int, but a type object was passed. Did
you forget a .new?
in block <unit> at -e:1
I did some reading and it looks like this is not a bug after all. From S06:
"Missing optional arguments default to their default values, or to an undefined
value if they have no default." In this case $bar defaults to (Int) and the
type check is applied to this default value. Therefore the where clause is
comparing a type object to 0, like so:
$ perl6 -e 'say Int >= 0'
Invocant requires an instance of type Int, but a type object was passed. Did
you forget a .new?
in block <unit> at -e:1
I've found two older tickets for the same problem (both rejected with 'not a
bug'):
* https://rt.perl.org/Ticket/Display.html?id=76514
* https://rt.perl.org/Ticket/Display.html?id=109182
In both tickets it is argued that type checks apply to default values as well.
To prevent the above failure one could either provide a defined default value
or check for an undefined value in the constraint:
$ perl6 -e 'subset UInt of Int where * >= 0; sub foo (UInt $bar? = 0) { say
"hi" }; foo()'
hi
$ perl6 -e 'subset UInt of Int where !.defined || * >= 0; sub foo (UInt $bar?)
{ say "hi" }; foo()'
hi
I'm rejecting this ticket. Please reopen if you don't agree with the above
reasoning.
