Title: Craft beautiful code with Ruby DSL Author: Ashrafuzzaman Event: RubyConf Bangladesh 2017 Date: 22 April 2017 Location: UGC Auditorium, Dhaka

1. Ruby DSL
Crafting beautiful code

2. You know basic Ruby
OR get you interested to know Ruby
Feel free to ask questions
Will only scratch the surface
After this, you can write a basic Ruby DSL
Expectations

3. DSL !!!

4. describe '#destroy'
context 'when resource is found'
it 'has 200 status code if logged in'
expect response to respond with 200
end
end
end
DSL ???
Test
X

5. DSL you might have seen in Ruby
describe '#destroy' do
context 'when resource is found' do
it 'has 200 status code if logged in' do
expect(response).to respond_with 200
end
end
end
RSpec

6. DSL you might have seen in Ruby
create_table :users do |t|
t.string :name
t.attachment :avatar
t.timestamps
end
DB Migrations

7. DSL you might have seen in Ruby
Rails.application.routes.draw do
root 'pages#home'
resources :pages, only: [:index, :show]
end
Rails Routing

8. What is DSL??
API that is tailored to
express Domain Logic

9. Language
VS
DSL

10. Why DSL ???
Simple to express
Embraces domain in code
Powerful abstraction that allows you to
change

11. Let’s start

12. Keys to Ruby DSL
Code blocks
instance_eval

13. Code blocks

14. Ruby code block
def report
puts "Header"
yield
puts "Footer"
end
report do
puts "From block"
end
Code Output
Header
From block
Footer
REPL

15. instance_eval

16. class Report
def initialize(&block)
puts "Header"
instance_eval &block
puts "Footer"
end
end
Report.new do
puts "From block"
end
Ruby instance_eval

17. class Report
def initialize(&block)
puts "Header"
instance_eval &block
puts "Footer"
end
def my_print(str)
puts str
end
end
Ruby instance_eval - 02
Report.new do
my_print "From block"
end
REPL

18. class Report
def initialize(data, &block)
@data = data; @columns = []
instance_eval &block
end
def column(column_name) @columns << column_name end
def print
@data.each { |row| @columns.each { |column| puts row[column] } }
end
end
Ruby instance_eval - 03

19. data = [
{name: 'Jitu', age: 34},
{name: 'Razeen', age: 3}
]
report = Report.new(data) do
column :name
end
report.print()
Ruby instance_eval - 03
Jitu
Razeen
REPL

20. My experience
In one of the rails project I worked on had a tons of reports, which needed the
following features
Queries, which are easy to understand and change
Filters
Pagination
Generate PDF, CSV, and email those reports
Generate graph in HTML and in PDF

21. DSL for generating reports
def index
reporter(Invoice.scoped) do
filter :title, type: :text
filter :created_at, type: :date
column :title { |invoice| link_to invoice.title, invoice }
column :total_paid, show_total: true
column :total_charged, show_total: true
column :paid
end
end

22. Demo

23. Author
A.K.M. Ashrafuzzaman
Software Engineer,
Newscred.
http://ashrafuzzaman.github.io

24. References
Link to this slide
Blogs
DSL QandA by Martin Fowler
Creating a Ruby DSL, by Leigh Halliday
Source code
Source codes for this slide
query_report gem