The Basis of Making DSL with Ruby

The Basis of Making DSL with Ruby 2010 8 28

Who I am • Yasuko Ohba • Ruby Programmer • Developing rails applications and iPhone applications • Everyleaf Corporation 2010 8 28

Housekeeping Book on Web Kozuchi • http://www.kozuchi.net • http://github.com/everyleaf/kozuchi 2010 8 28

• @nay3 (twitter) • http://github.com/nay • y.ohba@everyleaf.com 2010 8 28

2010 8 28

Ruby is good for DSL 2010 8 28

Domain Speciﬁc Language 2010 8 28

DSL 2010 8 28

DSL Hospitals 2010 8 28

Libraries DSL Hospitals 2010 8 28

Libraries Game DSL Hospitals 2010 8 28

Libraries Game DSL Hospitals EC 2010 8 28

It looks like a language rather than a program 2010 8 28

DSL 2010 8 28

internal DSL 2010 8 28

external internal DSL 2010 8 28

internal DSL in Ruby 2010 8 28

DSL examples • Rails • routes.rb • migrations • RJS • RSpec • Rake 2010 8 28

DSL-like codes : Rails class NotesController before_ﬁlter :ﬁnd_group ... end 2010 8 28

before_ﬁlter :ﬁnd_group 2010 8 28

It doesn’t look like DSL ? 2010 8 28

it can be less DSL like self.add_before_ﬁlter_methods( :ﬁnd_group) 2010 8 28

much more DSL like self.add_before_filter_methods( :find_group) before_filter :find_group 2010 8 28

My talk is simple 2010 8 28

I’ll talk about readable codes 2010 8 28

DSL-like codes : migrations create_table :users do |t| t.string :name t.timestamps end 2010 8 28

DSL-like codes : RSpec describe Group do it “name ” do g = Group.new g.should_not be_valid end 2010 8 28

Easy to read 2010 8 28

Easy to write 2010 8 28

Brief 2010 8 28

Easy to maintain 2010 8 28

OK, but... 2010 8 28

Do we just use existing great DSLs ? Photo by Lawrence OP 2010 8 28

NO 2010 8 28

Write your ruby codes like DSL everyday 2010 8 28

That’s just a skill of programming in Ruby 2010 8 28

I’m going to talk about 2010 8 28

..how to make your codes like DSL 2010 8 28

Our goal 2010 8 28

DSL-likeness 2010 8 28

What decides whether it is DSL or not ? 2010 8 28

No Solid Boundary 2010 8 28

But we can feel it 2010 8 28

to make the difference clear 2010 8 28

Compare normal Ruby codes and DSLs 2010 8 28

Normal Ruby Style “Hey receiver, do/return THIS !” 2010 8 28

Hey receiver do THIS! array.clear array[1] array.collect!{...} hash.delete(key) string.empty? 2010 8 28

Because it’s OOP 2010 8 28

DSLs have another styles 2010 8 28

3 typical forms 2010 8 28

1.Declarative Programming 2.Using Blocks 3.Methods Represent Special Concepts 2010 8 28

1. Declarative Programming 2010 8 28

“I am a rubyist” 2010 8 28

examples : declarative expression validates_presence_of :name before_ﬁlter ... has_many :children 2010 8 28

typical features • describe status or nature • receivers are not always important • no brackets 2010 8 28

No money self.money = 0 2010 8 28

No money self.money = 0 poor 2010 8 28

Mostly in Class Deﬁnitions 2010 8 28

No money class Boy poor ... end 2010 8 28

Try to express your request as a nature of the class 2010 8 28

Object task task task 2010 8 28

the class has this nature Object task task task 2010 8 28

Modules are good to express natures Class Object 2010 8 28

Modules are good to express natures Class Object Module 2010 8 28

Modules are good to express natures Class Object Module Module 2010 8 28

implementation 2010 8 28

Example 1 Declare the class to have some nature implemented as a module 2010 8 28

Book (Class) class Book include "Product" ... end Product 2010 8 28

class Book include "Product" ... end class Book acts_as_product ... end 2010 8 28

class Book acts_as_product ... end NameError: undeﬁned local variable or method `acts_as_product' for Book:Class 2010 8 28

You need acts_as_product method 2010 8 28

in the super class 2010 8 28

Book Object (Class) (Class) acts_as_product 2010 8 28

Book Object (Class) (Class) acts_as_product Product 2010 8 28

the easier way class Object def self.acts_as_product include Product end end the caller (Book) will be self here 2010 8 28

Book (Class) class Book acts_as_product ... end Product 2010 8 28

class Object def self.acts_as_product include Product end end Execute this before acts_as_product is invoked Rails conﬁg/initializer/acts_as_product.rb 2010 8 28

the softer way module ActsAsProduct module ClassMethods def acts_as_product include Product end end def self.included(base) base.extend(ClassMethods) end end Object.instance_eval { include ActsAsProduct } 2010 8 28

Object (Class) ActsAsProduct 2010 8 28

Object (Class) add ActsAsProduct acts_as_product ClassMethods 2010 8 28

Book Object (Class) (Class) add ActsAsProduct acts_as_product ClassMethods 2010 8 28

Book Object (Class) (Class) call acts_as_product add ActsAsProduct acts_as_product ClassMethods 2010 8 28

Book Object (Class) (Class) call acts_as_product add ActsAsProduct acts_as_product Product ClassMethods 2010 8 28

Example 2 set @title for a layout in some actions in Rails controllers 2010 8 28

Request Controller index show new edit @title layout 2010 8 28

want to write like this class BooksController < ApplicationController title " ", :only => [:edit, :update] .... end 2010 8 28

Same Strategy 2010 8 28

add a class method in the super class 2010 8 28

ApplicationController title BooksController 2010 8 28

ApplicationController class ApplicationController < ... def self.title ... end end 2010 8 28

title " ", :only => [:edit, :update] 2010 8 28

ApplicationController class ApplicationController < ... attr_accessor :title def self.title(name, options={}) before_ﬁlter(options) {|controller| controller.title = name} end ..... 2010 8 28

English naming problems validate ? validates ? 2010 8 28

2. Using Blocks 2010 8 28

examples : rake namespace :myapp do task :my_rake_task do # rake end end 2010 8 28

Example : Rails Form Helper form_for :book do |f| f.text_ﬁeld :name f.submit end 2010 8 28

Usages of block for DSL • describe complex structure • get some tasks into a scope 2010 8 28

describe structure 2010 8 28

Example 3 Write a game rule using playing cards 2010 8 28

Sevens game 'sevens' do |g| g.use 53 g.deal 53, :to => :each_player ... end 2010 8 28

Top You Level Game game use deal 2010 8 28

class Game def use (card_size, options ={}) ... end def deal (card_size, options ={}) ... end end 2010 8 28

def game g = Game.new yield g end 2010 8 28

Top Game You Level 2010 8 28

Top Game You Level game Block 2010 8 28

Top Game You Level game new Block 2010 8 28

Top Game You Level use game new deal Block 2010 8 28

want the block parameter removed? 2010 8 28

without parameter g game 'sevens' do use 53 deal 53, :to => :each_player ... end 2010 8 28

use instance_exec def game(&block) g = Game.new g.instance_exec(&block) end 2010 8 28

can be changed slightly game 'sevens' do uses 53 deals 53, :to => :each_player ... end 2010 8 28

3. methods represent special concepts 2010 8 28

methods that work as noun 2010 8 28

methods that represent vocabularies in another language 2010 8 28

books_url f.submit page.assert session request current_user 2010 8 28

an extra DSL style 2010 8 28

4. Methods to make codes like English 2010 8 28

should it years_since bytes from_now 2010 8 28

Balance REALLY Cosmos Useful ? of OOP 2010 8 28

General Tips 2010 8 28

General Tips • provide default values for parameters • use a hash parameter • use symbols • naming methods nicely 2010 8 28

Summary 2010 8 28

DSL is not very special 2010 8 28

Implementation will improve with DSL ideas 2010 8 28

Have a try ! 2010 8 28

The best way to learn is reading codes 2010 8 28

Thank you ! 2010 8 28

The Basis of Making DSL with Ruby

by nay on Aug 27, 2010

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