The document discusses the lack of a standard boolean class in Perl 5 and proposes two new candidates - bool.pm and Types::Bool - to address this issue. It provides background on how booleans are typically implemented in Perl 5 without a native type, challenges with existing solutions, and why a standard boolean class would help with serialization and interoperability. The bottom line is that any new solution needs to work well with existing Perl modules.

1. Common Boolean Class
for Perl 5
Kenichi Ishigaki
@charsbar
TPC in Glasgow 2018
Aug 16, 2018

2. me
• DBD::SQLite
• CPANTS
• PAUSE on Mojolicious
• JSON/JSON::PP
• Text::CSV/Text::CSV_PP

3. Boolean is really simple
It has only two states:
TRUE or FALSE

4. Boolean in Perl 5 is not
that simple
Because we don't have native boolean

5. Typical implementation of
boolean in Perl 5
my $true = 1;
my $false = 0;
$T = bless $true, $boolean_class;
$F = bless $false, $boolean_class;
(with some overload configuration)

6. What if a "boolean" object
is embedded in a string?
• use overload to convert them into
"true" or "false"?
• ... if "$false"; # but true
• say "This is " .
($bool->isa($boolean_class)
? ($bool ? "true" : "false")
: $bool); # ugly

7. How can you tell if
it's a boolean?
• MetaCPAN returns 1877 results
when you search "Bool"...
• Not all of them represent
boolean, though...

8. Don't worry too much
All of them should work in
the Perl context, at least
as long as you use them in
the boolean context

9. Until you start
serializing your data
JSON modules only accept
JSON::PP::Boolean objects
(or their aliases) by default

10. Luckily JSON::PP::Boolean
is in Perl 5 core now
• You can use it as a default
boolean class
• Do you want to use JSON::PP
just to get boolean objects?

11. How about boolean.pm?
• It would have been nice if it were
more widely adopted
• Unfortunately it is not supported
by JSON modules by default

12. Or Types::Serialiser?
• It provides boolean objects that are
JSON::PP::Boolean
• It has a more neutral name for CBOR::XS
• It's not in core, so it's hard to adopt for
toolchain modules or the likes

13. Then what to do?
• Add something into core?
• Or just use the same
convention under the hood?
• Or else?

14. The bottomline
• The new stuff should work
with existing modules
• Otherwise you can't use it
for interoperability

15. Two new candidates

16. bool.pm
• Written by Tina Mueller as a
proof of concept at PTS 2018
• Not yet CPANized
https://github.com/perlpunk/bool-p5/tree/json-pp-compat

17. Types::Bool
• Written by Adriano Ferreira,
inspired by Tina's PTS report
• Works quite similar to
Types::Serialiser
https://metacpan.org/pod/Types::Bool

18. There are still issues
to be solved
• bool namespace and Perl 6?
• Types:: namespace is reserved
for a different purpose?
• duplicated effort?
• and probably more

19. Further reading
• "My report of the Perl Toolchain Summit
2018 in Oslo" by Tina Mueller
http://blogs.perl.org/users/tinita/2018/05/my-report-of-the-
perl-toolchain-summit-2018-in-oslo.html
• "[Work in Progress] Boolean support with
Types::Bool"
https://github.com/makamaka/JSON-PP/pull/36

20. Let us know
your thoughts

21. Thanks