Also the innards of the function are kinda odd. You need to assign lines to $_ rather than returning them. I can understand why they did it that way, but it's pretty strange.
perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'
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[d/l] |
So instead of returning (undef, sub{...}) I should've just returned (sub {...}).
The documentation is correct, returning your way might work, but is wrong according to the documentation. Instead I guess the important part you made wrong before is not returning a reference to a scalar for source code prefix as element 1. This is what I've been struggling with, which resulted in strange behaviour, like the returned filehandle in my returned list got read once, but not for a second file and such. Instead of returning a reference to a scalar, I tried to return undef, \'' or plain '', which all failed. When I started to really use a scalar, the return worked as documented: The file in my case got read using the handle and I could warn each line read in the given sub. It's important as well to really end the reading with 0 in the sub, else Perl will try to read data in some endless loop.
my $prefix = ''; # undef is valid as well
return (\$prefix, IO::File->new($path, '<:bytes'),
sub { $_ =~ /^1;\s*$/ ? 0 : 1 }, undef);
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