Slide 1

Slide 1 text

Ruby Metaprogramming Sergio Gil (@porras)

Slide 2

Slide 2 text

No content

Slide 3

Slide 3 text

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

Slide 4

Slide 4 text

No content

Slide 5

Slide 5 text

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

Slide 6

Slide 6 text

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

Slide 7

Slide 7 text

Yukihiro Matsumoto ‘Matz’, Ruby creator

Slide 8

Slide 8 text

No content

Slide 9

Slide 9 text

Metaprogramming

Slide 10

Slide 10 text

defining metaprogramming

Slide 11

Slide 11 text

No content

Slide 12

Slide 12 text

No content

Slide 13

Slide 13 text

No content

Slide 14

Slide 14 text

No content

Slide 15

Slide 15 text

Classes Instances Methods Variables Constants Modules

Slide 16

Slide 16 text

Classes Instances Methods Variables Constants Modules

Slide 17

Slide 17 text

Memory

Slide 18

Slide 18 text

Classes Instances Methods Variables Constants Modules

Slide 19

Slide 19 text

No content

Slide 20

Slide 20 text

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

Slide 21

Slide 21 text

>> str = "hola" => "hola" >> str.methods => [..., :reverse, ...]

Slide 22

Slide 22 text

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

Slide 23

Slide 23 text

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

Slide 24

Slide 24 text

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

Slide 25

Slide 25 text

Ruby Object Model: The Musical

Slide 26

Slide 26 text

No content

Slide 27

Slide 27 text

No content

Slide 28

Slide 28 text

No content

Slide 29

Slide 29 text

No content

Slide 30

Slide 30 text

No content

Slide 31

Slide 31 text

It’s all about DRYness

Slide 32

Slide 32 text

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

Slide 33

Slide 33 text

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

Slide 34

Slide 34 text

Is that all?

Slide 35

Slide 35 text

Let Ruby create your methods for you

Slide 36

Slide 36 text

class Company [:projects, :people, ...].each do |method| eval %Q{ def #{method} HTTP::Request.new('/#{method}').get end } end end

Slide 37

Slide 37 text

class Company [:projects, :people, ...].each do |method| define_method method do HTTP::Request.new("/#{method}").get end end end

Slide 38

Slide 38 text

No content

Slide 39

Slide 39 text

It’s all about expresivity

Slide 40

Slide 40 text

No content

Slide 41

Slide 41 text

module HTTP def get(*methods) methods.each do |method| define_method method do HTTP::Request.new("/#{method}").get end end end end

Slide 42

Slide 42 text

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

Slide 43

Slide 43 text

“I Taw a Putty DSL...”

Slide 44

Slide 44 text

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

Slide 45

Slide 45 text

It’s all about flexibility

Slide 46

Slide 46 text

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

Slide 47

Slide 47 text

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

Slide 48

Slide 48 text

It’s all common sense

Slide 49

Slide 49 text

metaprogramming == programming

Slide 50

Slide 50 text

same trade-offs apply

Slide 51

Slide 51 text

No content

Slide 52

Slide 52 text

No content

Slide 53

Slide 53 text

No content

Slide 54

Slide 54 text

“Cleverness cannot win. The only weapons we have are simplicity and convention” http://alarmingdevelopment.org/?p=422

Slide 55

Slide 55 text

Thank you :)