Use bare double underscores instead of atoms

lib/koans/06_structs.ex

@@ -7,34 +7,34 @@ defmodule Structs do
 
   koan "Structs are defined and named after a module" do
     person = %Person{}
-    assert person == :__
+    assert person == __
   end
 
   koan "You can access the fields of a struct" do
     nobody = %Person{}
-    assert nobody.age == :__
+    assert nobody.age == __
   end
 
   koan "You can pass initial values to structs" do
     joe = %Person{name: "Joe", age: 23}
-    assert joe.name == :__
+    assert joe.name == __
   end
 
   koan "Update fields with the pipe '|' operator" do
     joe = %Person{name: "Joe", age: 23}
     older = %{ joe | age: joe.age + 10}
-    assert  older.age == :__
+    assert older.age == __
   end
 
   koan "The original struct is not affected by updates" do
     joe = %Person{name: "Joe", age: 23}
-    assert %{ joe | age: joe.age + 10}.age == :__
-    assert joe.age == :__
+    assert %{ joe | age: joe.age + 10}.age == __
+    assert joe.age == __
   end
 
   koan "You can pattern match into the fields of a struct" do
     %Person{age: age} = %Person{age: 22, name: "Silvia"}
-    assert age == :__
+    assert age == __
   end
 
   defmodule Plane do
@@ -45,14 +45,14 @@ defmodule Structs do
   def plane?(_), do: false
 
   koan "Or onto the type of the struct itself" do
-    assert plane?(%Plane{passengers: 417, maker: :boeing}) == :__
-    assert plane?(%Person{}) == :__
+    assert plane?(%Plane{passengers: 417, maker: :boeing}) == __
+    assert plane?(%Person{}) == __
   end
 
 
   koan "Are basically maps" do
     silvia = %Person{age: 22, name: "Silvia"}
 
-    assert Map.fetch!(silvia, :age) == :__
+    assert Map.fetch!(silvia, :age) == __
   end
 end