Merge pull request #124 from elixirkoans/protocols

Protocols

lib/koans/16_protocols.ex

@@ -0,0 +1,51 @@
+defmodule Protocols do
+  use Koans
+
+  @intro "Wan't to follow the rules? Adhere to the protocol!"
+
+  defprotocol School, do: def enrol(person)
+
+  defimpl School, for: Any do
+    def enrol(_) do
+      "Pupil enrolled at school"
+    end
+  end
+
+  defmodule Student do
+    @derive School
+    defstruct name: ""
+  end
+
+  defmodule Musician, do: defstruct name: "", instrument: ""
+  defmodule Dancer,  do: defstruct name: "", dance_style: ""
+  defmodule Baker, do: defstruct name: ""
+
+  defimpl School, for: Musician do
+    def enrol(musician) do
+      "#{musician.name} signed up for #{musician.instrument}"
+    end
+  end
+
+  defimpl School, for: Dancer do
+    def enrol(dancer), do: "#{dancer.name} enrolled for #{dancer.dance_style}"
+  end
+
+  koan "Sharing an interface is the secret at school" do
+    musician = %Musician{name: "Andre", instrument: "violin"}
+    dancer = %Dancer{name: "Darcy", dance_style: "ballet"}
+
+    assert School.enrol(musician) == ___
+    assert School.enrol(dancer) == ___
+  end
+
+  koan "Sometimes we all use the same" do
+    student = %Student{name: "Emily"}
+    assert School.enrol(student) == ___
+  end
+
+  koan "If you don't comply you can't get in" do
+    assert_raise ___, fn ->
+      School.enrol(%Baker{name: "Delia"})
+    end
+  end
+end