Implement access protocol for BitString

lib/elixir/lib/access.ex

@@ -8,10 +8,10 @@ defprotocol Access do
   invokes the `Access.access` protocol.
 
   This protocol is limited and is implemented only for the
-  following built-in types: keywords, records and functions.
+  following built-in types: keywords, records, functions and bitstrings.
   """
 
-  @only [List, Function, Record, Atom]
+  @only [List, Function, Record, Atom, BitString]
 
   @doc """
   Receives the element being accessed and the access item.
@@ -62,3 +62,13 @@ defimpl Access, for: Function do
     function.(item)
   end
 end
+
+defimpl Access, for: BitString do
+  @doc """
+  The access protocol for bitstrings invokes
+  String.at/2.
+  """
+  def access(string, position) when is_integer(position) do
+    String.at(string, position)
+  end
+end

lib/elixir/test/elixir/access_test.exs

@@ -19,6 +19,16 @@ defmodule AccessTest do
     assert function[:bar] == false
   end
 
+  test :bitstring do
+    assert "abc"[1] == "b"
+    assert "がガちゃ"[2] == "ち"
+    assert <<1, 2>>[1] == <<2>>
+    assert "abc"[3] == nil
+    assert "がガちゃ"[4] == nil
+    assert <<1, 2>>[2] == nil
+    assert <<1, 2, 3>>[-1] == <<3>>
+  end
+
   # Test nil at compilation time does not fail
   # and that @config[:foo] has proper precedence.
   nil = @config[:foo]