Remove empty? from the Enum protocol, closes #1097

Author: José Valim

lib/elixir/lib/enum.ex

@@ -48,11 +48,6 @@ defprotocol Enum.Iterator do
   """
   def iterator(collection)
 
-  @doc """
-  The function used to check if the collection is empty.
-  """
-  def empty?(collection)
-
   @doc """
   The function used to check if a value exists within the collection.
   """
@@ -87,22 +82,6 @@ defmodule Enum do
   @type index :: non_neg_integer
   @type default :: any
 
-  @doc """
-  Returns true if the `collection` is empty, otherwise false.
-
-  ## Examples
-
-      iex> Enum.empty?([])
-      true
-      iex> Enum.empty?([1,2,3])
-      false
-
-  """
-  @spec empty?(t) :: boolean
-  def empty?(collection) do
-    I.empty?(collection)
-  end
-
   @doc """
   Checks if the `value` exists within the `collection`.
 
@@ -347,6 +326,29 @@ defmodule Enum do
     end
   end
 
+  @doc """
+  Returns true if the collection is empty, otherwise false.
+
+  ## Examples
+
+      iex> Enum.empty?([])
+      true
+      iex> Enum.empty?([1,2,3])
+      false
+
+  """
+  @spec empty?(t) :: boolean
+  def empty?(collection) when is_list(collection) do
+    collection == []
+  end
+
+  def empty?(collection) do
+    case I.iterator(collection) do
+      { _iterator, pointer }  -> pointer == :stop
+      list when is_list(list) -> list == []
+    end
+  end
+
   @doc """
   Returns true if the first collection is equal to the second, every element in
   both collections is iterated through, as soon as an element differs, it
@@ -2161,9 +2163,6 @@ end
 defimpl Enum.Iterator, for: List do
   def iterator(list), do: list
 
-  def empty?([]), do: true
-  def empty?(_),  do: false
-
   def member?([], _),       do: false
   def member?(list, value), do: :lists.member(value, list)
 
@@ -2176,11 +2175,6 @@ defimpl Enum.Iterator, for: Function do
     { iterator, iterator.(first) }
   end
 
-  def empty?(function) do
-    { _iterator, first } = function.()
-    first == :stop
-  end
-
   def member?(function, value) do
     { iterator, first } = function.()
     do_member?(iterator.(first), iterator, value)

lib/elixir/lib/hash_dict.ex

@@ -580,7 +580,6 @@ end
 
 defimpl Enum.Iterator, for: HashDict do
   def iterator(dict),          do: HashDict.to_list(dict)
-  def empty?(dict),            do: HashDict.size(dict) == 0
   def member?(dict, { k, v }), do: match?({ :ok, ^v }, HashDict.fetch(dict, k))
   def member?(_dict, _),       do: false
   def count(dict),             do: HashDict.size(dict)

lib/elixir/lib/range.ex

@@ -26,10 +26,6 @@ defimpl Enum.Iterator, for: Range do
     { iterator, iterator.(first) }
   end
 
-  def empty?(Range[first: first] = range) do
-    Range.Iterator.count(first, range) < 1
-  end
-
   def member?(Range[first: first, last: last], value) do
     value in first..last
   end