Ruby Ate My DSL!

Presentation by Daniel Azuma at RubyConf 2019. Covers how DSLs can clash with "normal" Ruby code, and techniques for hardening a DSL against such conflicts.

Transcript

1. ruby ate
   my dsl!
   Daniel Azuma
   Google Cloud Platform
   Nov 18, 2019
   

   View Slide

2. # shell_app.rb
   require "sinatra"
   require "json"
   get "/" do
   output = invoke
   format_response output
   end
   def invoke
   `echo "this is the output"`
   end
   def format_response output
   JSON.dump({"output" => output})
   end
   

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3. # shell_app.rb
   require "sinatra"
   require "json"
   get "/" do
   output = invoke
   format_response output
   end
   def invoke
   `echo "this is the output"`
   end
   def format_response output
   JSON.dump({"output" => output})
   end
   

   View Slide

4. # shell_app.rb
   require "sinatra"
   require "json"
   get "/" do
   output = invoke
   format_response output
   end
   def invoke
   `echo "this is the output"`
   end
   def format_response output
   JSON.dump({"output" => output})
   end
   

   View Slide

5. # shell_app.rb
   require "sinatra"
   require "json"
   get "/" do
   output = invoke
   format_response output
   end
   def invoke
   `echo "this is the output"`
   end
   def format_response output
   JSON.dump({"output" => output})
   end
   

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6. # shell_app.rb
   require "sinatra"
   require "json"
   get "/" do
   output = invoke
   format_response output
   end
   def invoke
   `echo "this is the output"`
   end
   def format_response output
   JSON.dump({"output" => output})
   end
   LocalJumpError: no block given (yield)
   
   .../lib/sinatra/base.rb:1071:in `block in invoke'
   
   .../lib/sinatra/base.rb:1071:in `catch'
   
   .../lib/sinatra/base.rb:1071:in `invoke'
   
   shell_app.rb:7:in `block in '
   
   .../lib/sinatra/base.rb:1635:in `call'
   
   .../lib/sinatra/base.rb:1635:in `block in compile!'
   
   .../lib/sinatra/base.rb:987:in `block (3 levels) in route!'
   
   .../lib/sinatra/base.rb:1006:in `route_eval'
   
   .../lib/sinatra/base.rb:987:in `block (2 levels) in route!'
   
   .../lib/sinatra/base.rb:1035:in `block in process_route'
   
   .../lib/sinatra/base.rb:1033:in `catch'
   
   .../lib/sinatra/base.rb:1033:in `process_route'
   
   .../lib/sinatra/base.rb:985:in `block in route!'
   
   .../lib/sinatra/base.rb:984:in `each'
   
   .../lib/sinatra/base.rb:984:in `route!'
   
   .../lib/sinatra/base.rb:1097:in `block in dispatch!'
   
   .../lib/sinatra/base.rb:1071:in `block in invoke'
   
   .../lib/sinatra/base.rb:1071:in `catch'
   
   .../lib/sinatra/base.rb:1071:in `invoke'
   
   .../lib/sinatra/base.rb:1094:in `dispatch!'
   
   .../lib/sinatra/base.rb:919:in `block in call!'
   
   ...
   

   View Slide

7. # shell_app.rb
   require "sinatra"
   require "json"
   get "/" do
   output = invoke
   format_response output
   end
   def invoke
   `echo "this is the output"`
   end
   def format_response output
   JSON.dump({"output" => output})
   end
   LocalJumpError: no block given (yield)
   
   .../lib/sinatra/base.rb:1071:in `block in invoke'
   
   .../lib/sinatra/base.rb:1071:in `catch'
   
   .../lib/sinatra/base.rb:1071:in `invoke'
   
   shell_app.rb:7:in `block in '
   
   .../lib/sinatra/base.rb:1635:in `call'
   
   .../lib/sinatra/base.rb:1635:in `block in compile!'
   
   .../lib/sinatra/base.rb:987:in `block (3 levels) in route!'
   
   .../lib/sinatra/base.rb:1006:in `route_eval'
   
   .../lib/sinatra/base.rb:987:in `block (2 levels) in route!'
   
   .../lib/sinatra/base.rb:1035:in `block in process_route'
   
   .../lib/sinatra/base.rb:1033:in `catch'
   
   .../lib/sinatra/base.rb:1033:in `process_route'
   
   .../lib/sinatra/base.rb:985:in `block in route!'
   
   .../lib/sinatra/base.rb:984:in `each'
   
   .../lib/sinatra/base.rb:984:in `route!'
   
   .../lib/sinatra/base.rb:1097:in `block in dispatch!'
   
   .../lib/sinatra/base.rb:1071:in `block in invoke'
   
   .../lib/sinatra/base.rb:1071:in `catch'
   
   .../lib/sinatra/base.rb:1071:in `invoke'
   
   .../lib/sinatra/base.rb:1094:in `dispatch!'
   
   .../lib/sinatra/base.rb:919:in `block in call!'
   
   ...
   

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8. Domain-
   Specific
   Languages
   

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9. Daniel Azuma
   @danielazuma
   
   https://daniel-azuma.com/
   

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10. Daniel Azuma
    @danielazuma
    
    https://daniel-azuma.com/
    

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11. DSL:
    

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12. DSL:
    A set of “bare” methods that are
    not part of core Ruby
    

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13. # shell_app.rb
    require "sinatra"
    require "json"
    get "/" do
    output = invoke
    format_response output
    end
    def invoke
    `echo "this is the output"`
    end
    def format_response output
    JSON.dump({"output" => output})
    end
    

    View Slide

14. # shell_app.rb
    require "sinatra"
    require "json"
    get "/" do
    output = invoke
    format_response output
    end
    def invoke
    `echo "this is the output"`
    end
    def format_response output
    JSON.dump({"output" => output})
    end
    

    View Slide

15. # shell_app.rb
    require "sinatra"
    require "json"
    get "/" do
    output = invoke
    format_response output
    end
    def invoke
    `echo "this is the output"`
    end
    def format_response output
    JSON.dump({"output" => output})
    end
    method added to the
    “main” object
    

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16. View Slide

17. # routing.rb
    Rails.application.routes.draw do
    resources :brands, only: [:index, :show] do
    resources :products, only: [:index, :show]
    end
    resource :basket, only: [:show, :update, :destroy]
    resolve("Basket") { route_for(:basket) }
    end
    

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18. # routing.rb
    Rails.application.routes.draw do
    resources :brands, only: [:index, :show] do
    resources :products, only: [:index, :show]
    end
    resource :basket, only: [:show, :update, :destroy]
    resolve("Basket") { route_for(:basket) }
    end
    methods of the class
    ActionDispatch::Routing::Mapper
    

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19. # routing.rb
    Rails.application.routes.draw do
    resources :brands, only: [:index, :show] do
    resources :products, only: [:index, :show]
    end
    resource :basket, only: [:show, :update, :destroy]
    resolve("Basket") { route_for(:basket) }
    end
    methods of the class
    ActionDispatch::Routing::Mapper
    uses instance_eval to set self
    to a mapper instance
    

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20. DSL howto:
    • Add methods to an existing object
    
    • Change “self” within a block
    

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21. It’s Still Ruby!
    

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22. “nanospec”
    

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23. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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24. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    “describe” block
    

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25. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    “describe” block
    spec
    

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26. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    # nanospec.rb
    

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27. # nanospec.rb
    module Kernel
    def describe name, &block
    end
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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28. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    end
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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29. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    # nanospec.rb
    class Entity
    def initialize name
    @name = name
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    end
    end
    

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30. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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31. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    # nanospec.rb
    class Entity
    def initialize name
    @name = name
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    

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32. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    end
    def it name, &block
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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33. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    

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34. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    at_exit do
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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35. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    at_exit do
    @entities.each { |entity| entity.check }
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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36. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    at_exit do
    @entities.each { |entity| entity.check }
    end
    

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37. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    @name = "Ruby"
    puts "My name is #{@name}"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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38. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    at_exit do
    @entities.each { |entity| entity.check }
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    @name = "Ruby"
    puts "My name is #{@name}"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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39. # shell_app.rb
    require "sinatra"
    require "json"
    get "/" do
    output = invoke
    format_response output
    end
    def invoke
    `echo "this is the output"`
    end
    def format_response output
    JSON.dump({"output" => output})
    end
    LocalJumpError: no block given (yield)
    
    .../lib/sinatra/base.rb:1071:in `block in invoke'
    
    .../lib/sinatra/base.rb:1071:in `catch'
    
    .../lib/sinatra/base.rb:1071:in `invoke'
    
    shell_app.rb:7:in `block in '
    
    .../lib/sinatra/base.rb:1635:in `call'
    
    .../lib/sinatra/base.rb:1635:in `block in compile!'
    
    .../lib/sinatra/base.rb:987:in `block (3 levels) in route!'
    
    .../lib/sinatra/base.rb:1006:in `route_eval'
    
    .../lib/sinatra/base.rb:987:in `block (2 levels) in route!'
    
    .../lib/sinatra/base.rb:1035:in `block in process_route'
    
    .../lib/sinatra/base.rb:1033:in `catch'
    
    .../lib/sinatra/base.rb:1033:in `process_route'
    
    .../lib/sinatra/base.rb:985:in `block in route!'
    
    .../lib/sinatra/base.rb:984:in `each'
    
    .../lib/sinatra/base.rb:984:in `route!'
    
    .../lib/sinatra/base.rb:1097:in `block in dispatch!'
    
    .../lib/sinatra/base.rb:1071:in `block in invoke'
    
    .../lib/sinatra/base.rb:1071:in `catch'
    
    .../lib/sinatra/base.rb:1071:in `invoke'
    
    .../lib/sinatra/base.rb:1094:in `dispatch!'
    
    .../lib/sinatra/base.rb:919:in `block in call!'
    
    ...
    

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40. DSL
    

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41. TIP: Use a naming convention for instance
    variables and private methods
    

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42. TIP: Use a naming convention for instance
    variables and private methods
    # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    

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43. # nanospec.rb
    class Entity
    def initialize name
    @__name = name
    @__specs = {}
    end
    def it name, &block
    @__specs[name] = block
    end
    def check
    @__specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    TIP: Use a naming convention for instance
    variables and private methods
    

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44. # nanospec.rb
    class Entity
    def initialize name
    @__name = name
    @__specs = {}
    end
    def it name, &block
    @__specs[name] = block
    end
    def __check
    @__specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    TIP: Use a naming convention for instance
    variables and private methods
    

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45. With a DSL...
    There’s no such thing as “private”
    

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46. TIP: Delegate implementation to a
    separate object
    

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47. TIP:
    # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    at_exit do
    @entities.each { |entity| entity.check }
    end
    both the DSL and
    its implementation
    Delegate implementation to a
    separate object
    

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48. # nanospec.rb
    class EntityImpl
    def initialize name
    @name = name
    @specs = {}
    end
    def add name, block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    TIP:
    class EntityDSL
    def initialize impl
    @__impl = impl
    end
    def it name, &block
    @__impl.add name, block
    end
    end
    module Kernel
    def describe name, &block
    entity = EntityImpl.new name
    (@entities ||= []) << entity
    entity_dsl = EntityDSL.new entity
    entity_dsl.instance_eval &block
    end
    end
    at_exit do
    @entities.each { |entity| entity.check }
    end
    DSL only
    Implementation only
    Delegate implementation to a
    separate object
    

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49. TIP:
    class EntityDSL
    def initialize impl
    @__impl = impl
    end
    def it name, &block
    @__impl.add name, block
    end
    end
    module Kernel
    def describe name, &block
    entity = EntityImpl.new name
    (@entities ||= []) << entity
    entity_dsl = EntityDSL.new entity
    entity_dsl.instance_eval &block
    end
    end
    at_exit do
    @entities.each { |entity| entity.check }
    end
    DSL only
    # nanospec.rb
    class EntityImpl
    def initialize name
    @name = name
    @specs = {}
    end
    def add name, block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    Implementation only
    Delegate implementation to a
    separate object
    

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50. # nanospec.rb
    class EntityImpl
    def initialize name
    @name = name
    @specs = {}
    end
    def add name, block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    Implementation only
    TIP:
    class EntityDSL
    def initialize impl
    @__impl = impl
    end
    def it name, &block
    @__impl.add name, block
    end
    end
    module Kernel
    def describe name, &block
    entity = EntityImpl.new name
    (@entities ||= []) << entity
    entity_dsl = EntityDSL.new entity
    entity_dsl.instance_eval &block
    end
    end
    at_exit do
    @entities.each { |entity| entity.check }
    end
    DSL only
    Delegate implementation to a
    separate object
    

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51. # nanospec.rb
    class EntityImpl
    def initialize name
    @name = name
    @specs = {}
    end
    def add name, block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    TIP:
    class EntityDSL
    def initialize impl
    @__impl = impl
    end
    def it name, &block
    @__impl.add name, block
    end
    end
    module Kernel
    def describe name, &block
    entity = EntityImpl.new name
    (@entities ||= []) << entity
    entity_dsl = EntityDSL.new entity
    entity_dsl.instance_eval &block
    end
    end
    at_exit do
    @entities.each { |entity| entity.check }
    end
    DSL only
    Implementation only
    Delegate implementation to a
    separate object
    

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52. DSL
    

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53. DSL
    ❤
    

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54. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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55. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    module Kernel
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    at_exit do
    @entities.each { |entity| entity.check }
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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56. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    module NanospecDSL
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    extend NanospecDSL
    at_exit do
    @entities.each { |entity| entity.check }
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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57. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    module NanospecDSL
    def describe name, &block
    entity = Entity.new name
    (@entities ||= []) << entity
    entity.instance_eval &block
    end
    end
    extend NanospecDSL
    at_exit do
    @entities.each { |entity| entity.check }
    end
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    TIP: Add methods only where needed
    

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58. DSL
    ❤
    

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59. Helper methods
    

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60. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hi"
    end
    end
    describe "bar" do
    it "speaks" do
    puts "hello"
    end
    it "sleeps" do
    puts "zzz"
    end
    end
    

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61. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    puts "hello"
    end
    end
    

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62. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    

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63. private method of Object
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    

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64. # nanospec.rb
    class Entity
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    ...
    subclass of Object
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    

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65. # nanospec.rb
    class Entity < BasicObject
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    ...
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    BasicObject?
    

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66. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    FAIL
    # nanospec.rb
    class Entity < BasicObject
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    ...
    BasicObject?
    

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67. # nanospec.rb
    class Entity < BasicObject
    def initialize name
    @name = name
    @specs = {}
    end
    def it name, &block
    @specs[name] = block
    end
    def check
    @specs.each do |spec, block|
    puts "** #{@name} #{spec}"
    block.call
    end
    end
    end
    ...
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    TIP: BasicObject is usually NOT an effective
    base class for a DSL
    

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68. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    

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69. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    

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70. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    TIP: Design DSLs to honor lexical scoping
    

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71. # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    TIP: Design DSLs to honor lexical scoping
    method of singleton class
    block executed with
    instance_eval
    

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72. TIP: Design DSLs to honor lexical scoping
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    it "speaks" do
    try_speaking
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    describe "bar" do
    it "speaks" do
    try_speaking
    end
    def try_speaking
    puts "I'm a different object."
    end
    end
    separate scopes
    

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73. # nanospec_test.rb
    require "./nanospec.rb"
    describe "outer" do
    describe "inner" do
    it "speaks" do
    try_speaking
    end
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    TIP: Design DSLs to honor lexical scoping
    nested block
    

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74. # nanospec_test.rb
    require "./nanospec.rb"
    describe "outer" do
    describe "inner" do
    it "speaks" do
    try_speaking
    end
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    TIP: Design DSLs to honor lexical scoping
    delegate methods
    

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75. # nanospec_test.rb
    require "./nanospec.rb"
    describe "bar" do
    it "speaks" do
    try_speaking
    end
    it "sleeps" do
    puts "zzz"
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    

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76. Each “describe” block
    creates a class
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "bar" do
    it "speaks" do
    try_speaking
    end
    it "sleeps" do
    puts "zzz"
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    TIP: Consider modeling blocks as classes
    

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77. Each test is executed
    within a separate instance
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "bar" do
    it "speaks" do
    try_speaking
    end
    it "sleeps" do
    puts "zzz"
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    TIP: Consider modeling blocks as classes
    

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78. # nanospec_test.rb
    require "./nanospec.rb"
    describe "bar" do
    it "speaks" do
    try_speaking
    end
    it "sleeps" do
    puts "zzz"
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    Method of the
    described class
    TIP: Consider modeling blocks as classes
    

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79. # nanospec_test.rb
    require "./nanospec.rb"
    describe "bar" do
    it "speaks" do
    try_speaking
    end
    it "sleeps" do
    puts "zzz"
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    Method of the
    described class
    Use class_eval instead of
    instance_eval
    TIP: Consider modeling blocks as classes
    

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80. TIP: Consider modeling blocks as classes
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "bar" do
    it "speaks" do
    try_speaking
    end
    it "sleeps" do
    puts "zzz"
    end
    def try_speaking
    puts "testing 1...2...3..."
    end
    end
    

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81. Constants
    

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82. ≈
    ≈
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    MESSAGE = "Hello world!"
    it "speaks" do
    puts MESSAGE
    end
    end
    describe "bar" do
    MESSAGE = "Hello RubyConf!"
    it "speaks" do
    puts MESSAGE
    end
    end
    

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83. ≈
    # nanospec_test.rb
    require "./nanospec.rb"
    describe "foo" do
    MESSAGE = "Hello world!"
    it "speaks" do
    puts MESSAGE
    end
    end
    describe "bar" do
    MESSAGE = "Hello RubyConf!"
    it "speaks" do
    puts MESSAGE
    end
    end
    Constant redefined warning
    (both constants defined on
    Object)
    

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84. TIP: Provide alternatives to constants
    

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85. TIP: Provide alternatives to constants
    # rspec_example.rb
    require "rspec"
    describe "foo" do
    let(:message) { "Hello, world!" }
    it "speaks" do
    puts message
    end
    end
    describe "bar" do
    let(:message) { "Hello, RubyConf!" }
    it "speaks" do
    puts message
    end
    end
    

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86. View Slide

87. DSL
    

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88. Use a naming convention for instance
    variables and private methods
    Delegate implementation to a
    separate object
    DSL
    

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89. ❤
    DSL
    

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90. Add methods only where needed
    BasicObject is usually NOT an
    effective base class for a DSL
    Design DSLs to honor lexical scoping
    Consider modeling blocks as classes
    ❤
    DSL
    

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91. DSL
    

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92. DSL
    DSR
    (Domain-Specific Ruby)
    

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93. It’s Just Ruby!
    

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94. Daniel Azuma
    Google Cloud Platform
    @danielazuma
    
    https://daniel-azuma.com/
    ruby ate
    my dsl!
    

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