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Francesco Rodríguez @frodsan

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Metaprogramming: From Zero to Hero

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Use case

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on post, param("gem") do |params| if RubyGems.exists?(params["name"]) # add gem to the list. else # show error message. end end

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require "net/http" ! module RubyGems # ... ! def self.exists?(name) uri = URI(sprintf(URL, name)) res = Net::HTTP.get_response(uri) ! res.code == "200" end end

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test "creates if gem exists" do params = { "name" => "ricojson", "status" => "ok" } ! post("/gems", gem: params) ! assert_response(201) end

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module RubyGems def self.exists?(name) true end end ! test "creates if gem exists" do # ... end

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$ make test .

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test "errors if gem not exists" do post("/gems", gem: { name: "ruby" }) ! assert_response(422) end

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$ make test .F

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ఠ_ఠ ! • Stub. • Mock. • Spy.

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github.com/freerange/mocha >3000 LOC => ಥ_ಥ


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ʕ•ᴥ•ʔ ! • Minimalist. • Travel back in time. • No integration code. • No monkey patching.

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def stub(object, method, result) object.send(:define_method, method) do result end end

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test "creates if gem exists" do stub(RubyGems, :exists?, true) # ... end ! test "errors if gem not exists" do stub(RubyGems, :exists?, false) # ... end

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$ make test FF

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“Everything is an object”

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“Classes are also objects”

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>> Array.object_id # => 70214494875960 >> [].object_id # => 70214503361980

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struct RObject { struct RBasic basic; /* ... */ }; ! struct RClass { struct RBasic basic; /* ... */ struct st_table *m_tbl; VALUE super; };

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def stub(object, method, result) object.send(:define_method, method) do result end end

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Method Lookup Path

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foo = Foo.new foo.foo() foo Foo Object foo() foo()

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⊙﹏⊙ ! • Eigenclass. • Singleton class. • Object-specific class. • Virtual class. • Ghost class. • Metaclass. • Anonymous class.

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object = Object.new # => # ! ! object.singleton_class # => #> ! object.singleton_class.class # => Class

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bar = Foo.new ! def bar.foo "bar" end ! # or ! class << bar def foo "bar" end end

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bar.foo # => "bar" ! foo.foo # => "foo"

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bar Singleton Class Foo foo()

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$ make test FF

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def stub(object, method, result) metaclass = object.singleton_class ! metaclass.send(:define_method, method) do |*args| result end end

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$ make test ..

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test "errors if gem not exists" do stub(RubyGems, :exists?, false) # ... end ! RubyGems.exists?("false") # => false

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def stub(object, method, result) metaclass = object.singleton_class original = object.method(method) ! metaclass.send(:define_method, method) do |*args| result end ! yield ensure metaclass.send(:undef_method, method) metaclass.send(:define_method, method, original) end

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$ make test ..

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test "errors if gem not exists" do stub(RubyGems, :exists?, false) # ... end ! RubyGems.exists?("really-exists") # => ...

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github.com/frodsan/mocoso (‛ƅ㱼ƅ)‛ 22 LOC / 100 comment lines.


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Gracias! <3