Ruby Metaprogramming

Ruby Metaprogramming Sergio Gil (@porras)

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require 'excel' require 'sql' Excel.load('file.xls').each do |row| SQL.insert(row) end

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require 'html' require 'http' page = HTML.load(HTTP.get('http://example.com/')) page.links.each do |link|

HTTP.get(link).save end

class Company def projects HTTP::Request.new('/projects').get end def people HTTP::Request.new('/people').get end

def clients HTTP::Request.new('/clients').get end ... end

Yukihiro Matsumoto ‘Matz’, Ruby creator

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Metaprogramming

defining metaprogramming

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Classes Instances Methods Variables Constants Modules

Classes Instances Methods Variables Constants Modules

Memory

Classes Instances Methods Variables Constants Modules

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>> str = "hola" => "hola"

>> str = "hola" => "hola" >> str.methods => [...,

:reverse, ...]

>> str = "hola" => "hola" >> str.methods => [...,

:reverse, ...] >> def str.reverse "adios" end

>> str = "hola" => "hola" >> str.methods => [...,

:reverse, ...] >> def str.reverse "adios" end >> str.reverse

>> str = "hola" => "hola" >> str.methods => [...,

:reverse, ...] >> def str.reverse "adios" end >> str.reverse => "adios"

Ruby Object Model: The Musical

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It’s all about DRYness

class Company def projects HTTP::Request.new('/projects').get end def people HTTP::Request.new('/people').get end

... end

class Company def projects get('/projects') end def people get('/people') end

... private def get(url) HTTP::Request.new(url).get end end

Is that all?

Let Ruby create your methods for you

class Company [:projects, :people, ...].each do |method| eval %Q{ def

#{method} HTTP::Request.new('/#{method}').get end } end end

class Company [:projects, :people, ...].each do |method| define_method method do

HTTP::Request.new("/#{method}").get end end end

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It’s all about expresivity

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module HTTP def get(*methods) methods.each do |method| define_method method do

HTTP::Request.new("/#{method}").get end end end end

module HTTP def get(*methods) methods.each do |method| define_method method do

HTTP::Request.new("/#{method}").get end end end end class Company extend HTTP get :projects, :people, ... end

“I Taw a Putty DSL...”

class Company extend HTTP get :projects, :people, ... end

It’s all about flexibility

class Company def method_missing(method, *args, &blk) HTTP::Request.new("/#{method}").get end end

class Company def method_missing(method, *args, &blk) HTTP::Request.new("/#{method}").get end end

It’s all common sense

metaprogramming == programming

same trade-offs apply

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“Cleverness cannot win. The only weapons we have are simplicity

and convention” http://alarmingdevelopment.org/?p=422

Thank you :)