Perl5 meta programming
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This document discusses Perl 5 meta programming and provides examples of how to implement meta programming in Perl 5. It describes techniques like string eval, modifying the symbol table and typeglobs, using AUTOLOAD, Package::Stash, B:: modules, Class::Inspector, Class::Method::Modifiers, and Moo to get and set information about classes and define/modify methods and packages at runtime. It emphasizes writing tests and solving problems with existing modules when possible.
![string eval
• Preprocessing.
• Create minimized code by template.
(Apache::LogFormat::Compiler/Template-Toolkit)
• Define package/subroutine by program.
• Create something like an anonymous class.
(Moo::Role/Mo[uo]se::Role/etc…)
• And, more!!!](https://image.slidesharecdn.com/yapc2014-140830013556-phpapp02/85/Perl5-meta-programming-25-320.jpg)
![Mo[ou]se (Moo)
• Provides meta object protocol.
• Likes a Package::Stash.
• e.g.) add_method, remove_method, etc…
• Provides method modifiers.
• e.g.) before, after, around, etc…](https://image.slidesharecdn.com/yapc2014-140830013556-phpapp02/85/Perl5-meta-programming-44-320.jpg)
![Summary
• Get information from package.
• Class::Inspector/Package::Stash/symbol table
• and, meta object protocol (Mo[ou]se|Moo)
• Define methods or packages.
• Package::Stash/symbol table/meta object protocol.
• A last resort
• String eval.](https://image.slidesharecdn.com/yapc2014-140830013556-phpapp02/85/Perl5-meta-programming-46-320.jpg)
Perl5 meta programming
- 1. Perl5 meta programming YAPC::Asia 2014 id:karupanerura
- 2. NOTICE Sorry. I don’t speak in English. Because, I’m not good at English. So, maybe the wrong english has been many included.
- 3. about me • Kenta Sato • id:karupanerura • github/twitter/etc.. • Perl/JavaScript/Java/elisp… • CPAN Author • PAUSE ID: KARUPA • Mobile Factory, Inc. • Lead Engineer • Social Application
- 4. Rock’n’roll engineer The Monzllis
- 5. Gotanda.pm • Conference • #1 6/11 (Wed) • #2 9/17 (Wed) <= come on !!! • hash tag (twitter) • #gotandapm • http://gotanda-pm.github.io/
- 6. CPAN • TOML.pm • TOML::Parser • Locale::Scope • Parallel::Async
- 7. My YAPC::Asia history. • 2011 LT • 2012 LT + Individual Sponsor • 2013 Talk 20min + Individual Sponsor • 2014 Talk 40min + Individual Sponsor <= now • + Volunteer Staff • 2015 ???
- 8. “I wanna be the best speaker.” – karupanerura
- 9. Please vote for me!!
- 11. What is meta programming?
- 12. World of meta programming • Make a program by program. • Example: • Define subroutine by program. • Define package by program. • Call specified subroutine by a variable. • Rewrite AST by program. (not talk about it today.) • Called as “PL_check hack”. (XS)
- 13. Which is implemented by meta programming? • constant / Exporter / parent • Class::Accessor / Class::MOP (Moose) etc… • Class::Method::Modifiers • Module::Spy / Test::MockObject / Test::Mock::Guard • Apache::LogFormat::Compiler / Template-Toolkit • and more…
- 14. Perl5 has meta programming culture.
- 16. What do we get by meta programing? • Support to DRY • Inner DSL • And, readable code. • Preprocessing • And, faster processing.
- 17. In other words, freedom
- 18. “With freedom comes responsibility.” –Eleanor Roosevelt
- 19. What do we get by meta programing? • Incomprehension code. • Dirty inner DSL • Not readable. • Long, and long, and long time preprocessing. • Yep, you get slower code.
- 20. Usage of meta programming.
- 21. Meta programming is difficult. • Very freedom. • Yes. We can do anything! • Tend to the complex. • Difficult to analyze code by human. • You can’t know the process until execute. • It’s extreme.
- 22. But, Why we want meta programming? • Want to apply monkey patch. • But, Don’t want to rewrite source code. • We want to create many method. • But, There are similar almost. • Want to generate methods automatically.
- 23. Vital point • Write test scripts!!!!!!!!!!!!!!!!!!!!!!! • Solve the problem in existing modules. • as much as possible. • Create module as simply. • Give up when you can not be simple. • Think about more fundamental problem.
- 24. How to implement by meta programming. in perl5
- 25. string eval • Preprocessing. • Create minimized code by template. (Apache::LogFormat::Compiler/Template-Toolkit) • Define package/subroutine by program. • Create something like an anonymous class. (Moo::Role/Mo[uo]se::Role/etc…) • And, more!!!
- 26. string eval • Execute code by string. • Very freedom. • Very useful. • Be careful perl code injection attack. • So, do *NOT* use it if not needed.
- 27. string eval DEMO
- 28. UNIVERSAL • Base package of all packages.
- 29. UNIVERSAL DEMO
- 30. symbol talbe • e.g.) %main:: • Haves almost definition information of package. • Haves all typeglobs. • We can modify it. • Define (package|subroutine) by program.
- 31. typeglob • “a typeglob to hold an entire symbol table entry.”(from perldoc perldata) • *foo haves $foo and @foo and %foo.
- 32. symbol table & typeglob DEMO
- 33. AUTOLOAD • Fallback of subroutine call.
- 34. AUTOLOAD DEMO
- 35. Package::Stash • Provides symbol table modifier and accessor.
- 37. B.pm • Perl compiler backend. • Provides interface for access to inner data structure. • SV (PV|IV|NV|RV) / AV / HV / GV / CV / IO • e.g.) B::PV / B::IV / B::GV / B::CV / etc… • Provides many utility. (e.g. B::perlstring) • I'm not familiar. :0
- 38. B::svref_2object • Convert reference to B::* instance. • Access to inner information of object.
- 40. Class::Inspector • Provides to access information about a class and its structure • e.g.) methods, functions, etc…
- 42. Class::Method::Modifiers • Provides method modifiers. • e.g.) before, after, around, etc…
- 44. Mo[ou]se (Moo) • Provides meta object protocol. • Likes a Package::Stash. • e.g.) add_method, remove_method, etc… • Provides method modifiers. • e.g.) before, after, around, etc…
- 45. Moo DEMO
- 46. Summary • Get information from package. • Class::Inspector/Package::Stash/symbol table • and, meta object protocol (Mo[ou]se|Moo) • Define methods or packages. • Package::Stash/symbol table/meta object protocol. • A last resort • String eval.
- 47. Vital point AGAIN • Write test scripts!!!!!!!!!!!!!!!!!!!!!!! • Solve the problem in existing modules. • as much as possible. • Create module as simply. • Give up when you can not be simple. • Think about more fundamental problem.
- 48. Mobile Factory, Inc. • Using modern perl in many projects. • perl 5.18 + Carton + Amon2 + Starlet • perl 5.14 + Amon2 • Free vegetable juices and other something drinks. • Everyone available dual display. (22inch x 2)
- 49. ! Let’s work at Mobile Factory team!!
- 50. ! Thank you for listening!!
- 51. Any questions?