Code Generation: The Safety Scissors of Metaprogramming
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Metaprogramming is cool. Metaprogramming is hip. Metaprogramming has performance costs and is a serious pain in the butt to debug.You can get a lot of the benefits of metaprogramming from using code generation instead. In fact, most metaprogramming is really just dynamic code generation. Or maybe it’s the other way around. You could say that metaprogramming is really just dynamic code generation, or that code generation is just compiled metaprogramming. Code generation is code which creates text strings of code and saves them to the filesystem; metaprogramming is code which creates text strings of code and passes them directly to eval() or one of its variants.Either way you slice it, code generation is a powerful strategy. Using Ryan Davis’ awe-inspiring library Ruby2Ruby, it’s technically possible to unit test metaprogramming, but unit testing code generation is easier to do. Its results are also a lot easier to debug. Jack Herrington’s brilliant book “Code Generation In Action” demonstrates how you can generate the literally hundreds of Java files a non-trivial EJB application needs with a much smaller number of Ruby programs, slashing development time by months. Several aspects of Rails use code generation extensively, including scaffolding and the rails command itself. Rails’ core strategy of “convention over configuration” would be impossible without code generation.In this talk, I’ll demonstrate both how to unit-test metaprogramming with Ruby2Ruby, nd how to automate EJB application development with Herrington’s code generation techniques. Bring a nice Tupperware bowl to catch your brain in after it leaks out your ears.
Transcript of Code Generation: The Safety Scissors of Metaprogramming
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Ἀρχιμήδης2
π3
δος µοι πα στω, καιταν γαν κινάσω
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λ5
λthe ultimate
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μετά7
meta8
metaprogramming?
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metaOO
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Code GenerationThe Safety Scissors
Of Metaprogramming
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Ruby2Ruby12
(lambda do puts “hello world”end).to_ruby
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class Widget < ActiveRecord::Baseend
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Ruby2Ruby.translate(Widget)
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class Widget < ActiveRecord::Base has_one :fooend
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Ruby2Ruby.translate(Widget)
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overkil l
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monkeypatching
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tangledobject graph
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stop monkey-patching!
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nothing can ever protect you
from bad programming
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nothing can ever protect you
from bad programming
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tests
specs30
tests
specsy u need
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tests rawk
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debuggers suck
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debuggers suck
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monkey-patchmonkey-patching
itself
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meta-monkey-patching
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rubinius38
nodebox
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code == data
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at this point, I just demoed code from my blog.below is a link to the post:
http://gilesbowkett.blogspot.com/2008/03/simple-metaprogramming-logger-with.html(code samples are included)
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simple object graph
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nodebox
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tangledobject graph
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node box
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same tool
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different output
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proof of concept49
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foo
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foo
bar
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foo
barbaz
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foo
barbaz
foofoo
foo
foo
foo
foo
foo
bar
bar
bar
bar
bar
bar
barbaz
baz
baz
baz
baz
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debuggers suck
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some people want debuggers
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“Ruby has no tool support!”
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1 day
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shock the monkey
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Powerful Tools
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Powerful Tools
• Rubinius
• Nodebox
• code == data
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Powerful Tools
• Rubinius
• Nodebox
• code == data
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Powerful Tools
• Rubinius
• Nodebox
• code == data
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• Rubinius
• Nodebox
• code == data
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code == data
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1998
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generated HTML
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automated cvs and rcs
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(2003)EJB
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legacy app: 150 tables
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ejb: 7 files per entity
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7 * 150 = 1050 Java files
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by hand: 3+ man-years
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generators: 2 man-months
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four generator types
• code munger generator• inline code expansion generator• mixed-code generator• partial-class generator• tier generator
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generating UIs
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generating unit tests
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embedding SQLwith generators
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creating databaseaccess generators
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generating webservices layers
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generating models froma business logic DSL
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sound familiar?
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script/generate scaffold
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script/generate resource
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script/generate plugin
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script/generate migration
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script/generate
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rails Command
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acts_as_authenticated
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restful_authentication
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ActiveRecord SQL
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ActionPack Helpers•ActiveRecordHelper•AssetTagHelper•AtomFeedHelper•BenchmarkHelper•CacheHelper•CaptureHelper•DateHelper•DebugHelper•FormHelper•FormOptionsHelper
•FormTagHelper•JavascriptHelper•NumberHelper•PrototypeHelper•RecordTagHelper•SanitizeHelper•ScriptaculousHelper•TagHelper•TextHelper•UrlHelper
Text
•RecordIdentificationHelper
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code generation FTW
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code generation FTW
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code == data
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(eq (code (data)))
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functions which return functions which return functions which return functions which return functions which return functions which return functions which return functions which return functions which return functions which return functions which return functions which return functions
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code which generates data which runs as code which generates data which runs as code which generates data which runs as code which generates data which runs as code which generates data which runs as code which generates data which runs as code
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lisp macros pwn“metaprogramming”
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and you can dothem in Perl!
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shocked? perl!
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shocked? perl!
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λthe ultimate
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combinator113
$114
$small teams
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$small teams lisp macros
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great programmers canwrite better programmersthan they can hire
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great programmers canwrite better programmersthan they can hire
metaprogramming118
great?119
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intergalactic voluntarily baldclone wizards of time and space
who the womens are be lusting fors
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incredible power
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simpleclarity
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simplicity
magic127
skilled programmers canwrite better programmersthan they can hire
metaprogramming128
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code which generates data which runs as code which generates data which runs as code which generates data which runs as code which generates data which runs as code which generates data which runs as code which generates data which runs as code
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Unix.is_a? Lisp
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# => true
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δος µοι πα στω, καιταν γαν κινάσω
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Ruby.is_a? πα στω
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# => true
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boba fezz
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Caveats!
• read the book, the technique is easy
• leveraging it is the clever part
• you can use Ruby as well as Rubinius
• if Unix is a Lisp, the filesystem is a compiler
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Caveats!
• read the book, the technique is easy
• leveraging it is the clever part
• you can use Ruby as well as Rubinius
• if Unix is a Lisp, the filesystem is a compiler
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Caveats!
• read the book, the technique is easy
• leveraging it is the clever part
• you can use Ruby as well as Rubinius
• if Unix is a Lisp, the filesystem is a compiler
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Caveats!
• read the book, the technique is easy
• leveraging it is the clever part
• you can use Ruby as well as Rubinius
• if Unix is a Lisp, the filesystem is a compiler
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Caveats!
• read the book, the technique is easy
• leveraging it is the clever part
• you can use Ruby as well as Rubinius
• if Unix is a Lisp, the filesystem is a compiler
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Essential Technique
• read the book, the technique is easy
• leveraging it is the clever part
• you can use Ruby as well as Rubinius
• if Unix is a Lisp, the filesystem is a compiler
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Essential Technique
• puts
• leveraging it is the clever part
• you can use Ruby as well as Rubinius
• if Unix is a Lisp, the filesystem is a compiler
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Essential Technique
• puts
• eval
• you can use Ruby as well as Rubinius
• if Unix is a Lisp, the filesystem is a compiler
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Essential Technique
• puts
• eval
• ERB
• if Unix is a Lisp, the filesystem is a compiler
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Essential Technique
• puts
• eval
• ERB
• if Unix is a Lisp, the filesystem is a compiler•(unix pipes)
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Essential Technique
• open mouth
• make noise
• profit
• if Unix is a Lisp, the filesystem is a compiler
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