how to make dsl

DSL Powered by Rabbit 2.1.2

Yukio Gotosg.rb

2014/04/29

Who am I ?

Yukio Gotofavorite

Ruby, emacs, zsh, tennis✓✓

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

github

https://github.com/byplayer/

twitter

@byplayer

Today's target

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

What is 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

By the way

Did you make DSL ?

use only ?

Do you think

you can only use DSL?

NO !!!

your own DSL

Rubyis

easiest language

one of the most

easiest language

making 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✓

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

quite easy

Typing config

Typing 'conf.'

is not

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

Ruby's black magic

parsing

parsing it

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

MeetupLoader

make support class

define setter method

make support class

not use '='

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

default receiver

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

Ruby's black magic

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

Today,

talk about

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 ?

Thank you

Thank youfor listening

how to make dsl

dsl dsl

external dsl conguration

dsl yukio goto

external dsl sql

todays target use dsl

group conf

conf conf

path end mt end end

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