Metaprogramming: From Zero to Hero. (URU meetup)

How did I learn metaprogramming by creating a minimalist stubbing library called mocoso (https://github.com/frodsan/mocoso).

Transcript

2. Francesco Rodríguez @frodsan
3. Metaprogramming: From Zero to Hero
4. Use case
5. on post, param("gem") do |params| if RubyGems.exists?(params["name"]) # add gem to the list. else # show error message. end end
6. 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
7. test "creates if gem exists" do params = { "name" => "ricojson", "status" => "ok" } ! post("/gems", gem: params) ! assert_response(201) end
8. module RubyGems def self.exists?(name) true end end ! test "creates if gem exists" do # ... end
9. $ make test .
10. test "errors if gem not exists" do post("/gems", gem: { name: "ruby" }) ! assert_response(422) end
11. $ make test .F
13. ఠ_ఠ ! • Stub. • Mock. • Spy.
14. github.com/freerange/mocha >3000 LOC => ಥ_ಥ

15. ʕ•ᴥ•ʔ ! • Minimalist. • Travel back in time. • No integration code. • No monkey patching.
16. def stub(object, method, result) object.send(:define_method, method) do result end end
17. test "creates if gem exists" do stub(RubyGems, :exists?, true) # ... end ! test "errors if gem not exists" do stub(RubyGems, :exists?, false) # ... end
18. $ make test FF
19. “Everything is an object”
20. “Classes are also objects”
21. >> Array.object_id # => 70214494875960 >> [].object_id # => 70214503361980
22. struct RObject { struct RBasic basic; /* ... */ }; ! struct RClass { struct RBasic basic; /* ... */ struct st_table *m_tbl; VALUE super; };
23. def stub(object, method, result) object.send(:define_method, method) do result end end
24. Method Lookup Path
25. foo = Foo.new foo.foo() foo Foo Object foo() foo()
26. ⊙﹏⊙ ! • Eigenclass. • Singleton class. • Object-specific class. • Virtual class. • Ghost class. • Metaclass. • Anonymous class.
27. object = Object.new # => #<Object:…> ! ! object.singleton_class # => #<Class:#<Object:…>> ! object.singleton_class.class # => Class
28. bar = Foo.new ! def bar.foo "bar" end ! # or ! class << bar def foo "bar" end end
29. bar.foo # => "bar" ! foo.foo # => "foo"
30. bar Singleton Class Foo foo()
31. $ make test FF
32. def stub(object, method, result) metaclass = object.singleton_class ! metaclass.send(:define_method, method) do |*args| result end end
33. $ make test ..
34. test "errors if gem not exists" do stub(RubyGems, :exists?, false) # ... end ! RubyGems.exists?("false") # => false
35. 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
36. $ make test ..
37. test "errors if gem not exists" do stub(RubyGems, :exists?, false) # ... end ! RubyGems.exists?("really-exists") # => ...
38. github.com/frodsan/mocoso (‛ƅ㱼ƅ)‛ 22 LOC / 100 comment lines.

39. Gracias! <3