Ruby DSL

Ruby DSL
Crafting beautiful code

● 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

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

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

create_table :users do |t|
t.string :name
t.attachment :avatar
t.timestamps
end
DB Migrations

Rails.application.routes.draw do
root 'pages#home'
resources :pages, only: [:index, :show]
end
Rails Routing

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

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

Keys to Ruby DSL
Code blocks
instance_eval

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

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

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

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

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

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
● Had complex rowspan and colspan

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

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

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

Ruby DSL

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