How to make DSL

DSL Powered by Rabbit 2.1.2

DSL

Yukio Gotosg.rb

2014/04/29


Who am I ?

Yukio Gotofavorite

Ruby, emacs, zsh, tennis✓✓

workRakuten Asia Pte. Ltd.✓As senior application engineer✓

✓

✓


IDs

github

https://github.com/byplayer/

twitter

@byplayer


Today's target

use DSL -*-*-*-*-*-*- making DSL


DSL

What is DSL ?


DSL

DSL =Domain Specific

Language


external DSL

SQL✓

SELECT id, user_name FROM users


external DSL

configuration files✓

http { passenger_root /usr/local/rvm/gems/ruby-2.1.0/gems/passenger-4.0.29; passenger_ruby /usr/local/rvm/wrappers/ruby-2.1.0/ruby;

include mime.types; default_type application/octet-stream;

# ...}


internal DSL

Rails✓

class User < ActiveRecord::Base validates :name, presence: trueend


BTW

By the way


Did you make DSL ?

Did you make DSL ?


use only ?

Do you think

you can only use DSL?


No

NO !!!


You

You


can

can


make

make


your own DSL

your own DSL


AND

AND


Ruby

Rubyis


easiest language

one of the most

easiest language


making DSL

making DSL


How to make DSL

How to make DSL


before that

Before that


Benefit of making DSL

DSL makes your Applicationeasy to write✓easy to read✓easy to use✓

✓


theme

Configuration file using DSL


config version 1

# singapore-ruby-group.confmeetup do |conf| conf.group = 'Singapore-Ruby-Group' conf.organizer = 'Winston Teo' conf.sponsors = ['Engine Yard', 'Silicon Straits', 'Plug-In@Blk71']end


how to use

mt = Meetup.load('singapore-ruby-group.conf')

puts mt.group# => Singapore-Ruby-Group

puts mt.organizer# => Winston Teo

puts mt.sponsors.join(', ')# => Engine Yard, Silicon Straits, Plug-In@Blk71


implementation

# Sample class to load configurationclass Meetup attr_accessor :group, :organizer, :sponsors

def self.load(path) fail "config file not found: #{path}" unless File.exist?(path)

mt = Meetup.new File.open(path, 'r') do |file| mt.instance_eval(File.read(path), path) end

mt end

private

def meetup yield self endend


key point

def self.load # ... File.open(path, 'r') do |file| mt.instance_eval(File.read(path), path) end # ...end

def meetup yield selfend


first point

pass string to 'instance_eval'

def self.load # ... File.open(path, 'r') do |file| mt.instance_eval(File.read(path), path) end # ...end


instance_eval

"instance_eval"


instance_eval

interpretes String


instance_eval

as Ruby code


instance_eval

using Object context


instance_eval

In this case,


instance_eval

configuration file is


instance_eval

interpreted as


instance_eval

Meetup class source code


expand instance_eval virtually

def self.load # File.open(path, 'r') do |file| # mt.instance_eval(File.read(path), path) # end meetup do |conf| conf.group = 'Singapore-Ruby-Group' conf.organizer = 'Winston Teo' conf.sponsors = ['Engine Yard', 'Silicon Straits', 'Plug-In@Blk71'] endend


easy

quite easy


but

BUT


Typing config

Typing 'conf.'


is is

is not


sexy

sexy


Is it sexy ?

meetup do |conf| conf.group = 'Singapore-Ruby-Group' conf.organizer = 'Winston Teo' conf.sponsors = ['Engine Yard', 'Silicon Straits', 'Plug-In@Blk71']end


ideal configuration

# singapore-ruby-group.confmeetup { group 'Singapore-Ruby-Group' organizer 'Winston Teo' sponsors ['Engine Yard', 'Silicon Straits', 'Plug-In@Blk71']}


readable

readable✓

DRY✓


Let's use

Let's use


Ruby's black magic

Ruby's black magic


parsing

parsing it


load

class Meetup attr_accessor :group, :organizer, :sponsors

def self.load(path) mt = new File.open(path, 'r') do |file| loader = MeetupLoader.new(mt) loader.instance_eval(file.read, path) end

mt endend


make support class

make support class

MeetupLoader


make support class

define setter method


make support class

not use '='


make support class

and


make support class

load function(meetup) only


make support class (setter)

class MeetupLoader def initialize(mt) @meetup = mt end # ... def group(g) @meetup.group = g end

def organizer(o) @meetup.organizer = o end # ...end


instance_eval again

class MeetupLoader # ... def meetup(&block) instance_eval(&block) end # ...end


The point of black magic

instance_eval again


instance_eval for block

instance_eval with block


changes

changes


default receiver

default receiver


in the block

in the block


original code

class Meetup attr_accessor :group, :organizer, :sponsors

def self.load(path) mt = new File.open(path, 'r') do |file| loader = MeetupLoader.new(mt) loader.instance_eval(file.read, path) end

mt endend


expand instance_eval virtually 1

def self.load(path) mt = new File.open(path, 'r') do |file| loader = MeetupLoader.new(mt) # loader.instance_eval(file.read, path) loader.meetup { group 'Singapore-Ruby-Group' organizer 'Winston Teo' # ... } end #...



class MeetupLoader # ... def meetup(&block) instance_eval(&block) end # ...end



def meetup(&block) # instance_eval(&block) #{ self.group 'Singapore-Ruby-Group' self.organizer 'Winston Teo' # ... # }end


The trick

The trick


of

of


Ruby's black magic

Ruby's black magic


is

is






def meetup(&block) # instance_eval(&block) #{ self.group 'Singapore-Ruby-Group' self.organizer 'Winston Teo' # ... # }end


Today

Today,


I

I


don't

don't


talk about

talk about


caution points

caution points


caution points

security✓

handle method_missing✓handle syntax error✓


source code

https://github.com/byplayer/meetup_config✓https://github.com/byplayer/meetup_config_ex

✓


take a way

You can make DSL✓

instance_eval is interesting✓


Hiring

Rakuten Asia Pte. Ltd. wants to hire

Server side Application Engineer (Ruby, java)

✓

iOS, Android Application Engineer

✓

✓


Any question ?

Any question ?


Thank you

Thank youfor listening

Technology

How to make DSL