KWArgs — the killer Ruby feature you‘re not using

Keyword args have been with us since Ruby 2.0, yet they're not widely used. In this presentation, I explain how KWArgs are strictly better than positional: they enable you to write more loosely coupled and flexible code that is easier to read.

Transcript

1. KWArgs The killer ruby feature you’re not using* *Not really
2. Who I am • Software developer for 20 years • Ruby developer for 10 • Taught R**** bootcamp • R**** & Postgres consultant Guyren G Howe
 @unclouded
 guyren@relevantlogic.com
 http://relevantlogic.com Look for my forthcoming
 “Love your Database”
3. Outline • What it do • Clearer • More flexible • More functional
4. What it do def foo(x, y = 3, *rest, opt2:, opt1: nil, **c, &block) positional
 required arg positional
 optional arg kwarg optional kwarg required positional
 args splat kwargs splat* *Turns out to be super interesting
5. Pretty intuitive rect(x: 10, y: 20, width: 30) args = {x: 10, y: 20, width: 30}
 rect(args) rect(:x => 10, :y => 20, :width => 30)
6. Pretty intuitive def rect(x:, y:, width:, height: width, line_width: 1) defaults can reference
 earlier args
7. Pretty intuitive > h1 = {a: 1, b: 1} > h2 = {a: 2, c: 2} > {a: 0, **h1, **h2} => {:a=>2, :b=>1, :c=>2}
8. Caveats • positional args before kwargs • hash-value positional args can get tricky
9. Clearer Net::HTTP.new('server.com', 732, 'other_server.com', 872, 'admin', 'monkey123')
10. Clearer Net::HTTP.new(server: 'server.com', port: 732, proxy: 'other_server.com', proxy_port: 872,
 proxy_user: 'admin', proxy_pass: 'monkey123') Meh
12. Clearer Net::HTTP.new( server: 'server.com', port: 732, proxy: 'other_server.com', proxy_port: 872,
 proxy_user: 'admin', proxy_pass: 'monkey123' ) Clearer!
13. Clearer Net::HTTP.new( server: 'server.com', port: 732, proxy: 'other_server.com', proxy_port: 872,
 proxy_user: 'admin', proxy_pass: 'monkey123' ) Net::HTTP.new('server.com', 732, 'other_server.com', 872, 'admin', 'monkey123')
15. Clearer Net::HTTP.new( server: 'server.com', port: 732, proxy: 'other_server.com', proxy_port: 872,
 proxy_user: 'admin', proxy_pass: 'monkey123' )
16. More Flexible Net::HTTP.new( server: 'server.com', port: 732, proxy: 'other_server.com', proxy_port: 872,
 proxy_user: 'admin', proxy_pass: 'monkey123' )
17. More Flexible Net::HTTP.new( server: 'server.com', proxy: 'other_server.com', proxy_port: 872,
 proxy_user: 'admin', proxy_pass: 'monkey123' )
18. More Flexible Net::HTTP.new( server: 'server.com', port: 732, proxy_user: 'admin' )
19. More Flexible def render_table(rows:) … end class UsersController … render_table(rows: @users) end
20. More Flexible def render_table( rows:, headers: nil ) … end class CompaniesController … render_table( rows: @companies, headers: @companies.first.keys ) end
21. More Flexible def render_table( rows:, headers: nil, stripes: nil ) … end class OrdersController … render_table( rows: @orders, stripes: '#lightblue' ) end
22. vs Positional def render_table(rows, headers = nil, stripes = nil) … end class OrdersController … render_table(@orders, nil, '#lightblue') end
23. Lots of Parameters def render_table( rows:, headers: nil, stripes: nil, margin: '10px', border: '1px solid black', class: 'table' ) Why not?
24. “Loose Coupling”
25. “Dependency Injection”
26. What if? User.query( where: "name like 'harry%'", order: 'last_name ASC, first_name ASC', group: 'division_id', joins: 'division' )
27. Functional
28. def foo(x, y = 3, *rest, opt2:, opt1: nil, **c, &block) kwargs splat* *Turns out to be super interesting
29. Functional @user = User.find(user_params[:user_id]) @salary = calculate_salary( base: 20_000, per_mile: 10, **user.overrides )
30. Functional @user = User.find(user_params[:user_id]) company = @user.company @salary = calculate_salary( base: 20_000, per_mile: 10, **{**company.overrides, **user.overrides } ) Functional!
31. ‘Context Funnel’
32. Functional def foo(a:, b: 'B', **c) … end ‘c’ for ‘context’
33. Context Funnel Receive **c
 Pass on **c
34. More Flexible def index … render_table(rows: @users) end
35. More Flexible def index … render_table(rows: @users) end def render_table(rows:, **c) … rows.each do |row| render_row(row, **c) end end
36. More Flexible def render_row(row:, **c) content_tag('tr') do row.map do |k, v| content_tag('td') do render partial: 'cells/' + k.to_s, locals: {thing: v, **c} end.join('') end end
37. More Flexible … render partial: 'cells/' + k.to_s, locals: {thing: v, **c} … # views/cells/_last_name.html.erb <%= thing %>
38. More Flexible … render_table(rows: @users) … # views/cells/_last_name.html.erb <%= thing %>
39. More Flexible # views/cells/_last_name.html.erb <% last_name_format ||= ->{yield} %> <%= last_name_format(thing)%>
40. More Flexible def index … render_table( rows: @users, last_name_format: ->(){"<b>#{yield}</b>"} ) end # views/cells/_last_name.html.erb <% last_name_format ||= ->{yield} %> <%= last_name_format(thing)%> Flexible!
41. Clearer Net::HTTP.new( server: 'server.com', port: 732, proxy: 'other_server.com', proxy_port: 872,
 proxy_user: 'admin', proxy_pass: 'monkey123' ) Clearer!
42. Functional @user = User.find(user_params[:user_id]) company = @user.company @salary = calculate_salary( base: 20_000, per_mile: 10, **company.overrides .merge(user.overrides) ) Functional!
43. More Flexible def index … render_table( rows: @users, last_name_format: ->(){"<b>#{yield}</b>"} ) end # views/cells/_last_name.html.erb <% last_name_format ||= ->{yield} %> <%= last_name_format(thing)%> Flexible!
44. FIN Guyren G Howe guyren@relevantlogic.com @unclouded http://relevantlogic.com