Implemented Enumerator#peek for 1.9

kernel/common/enumerator.rb

@@ -159,40 +159,6 @@ def reset
       end
     end
 
-    # Returns the next object in the enumerator
-    # and move the internal position forward.
-    # When the position reached at the end,
-    # internal position is rewound then StopIteration is raised.
-    #
-    # Note that enumeration sequence by next method
-    # does not affect other non-external enumeration methods,
-    # unless underlying iteration methods itself has side-effect, e.g. IO#each_line.
-    #
-    def next
-      unless @generator
-        # Allow #to_generator to return nil, indicating it has none for
-        # this method.
-        if @object.respond_to? :to_generator
-          @generator = @object.to_generator(@iter)
-        end
-
-        if !@generator and gen = FiberGenerator
-          @generator = gen.new(self)
-        else
-          @generator = ThreadGenerator.new(self, @object, @iter, @args)
-        end
-      end
-
-      begin
-        return @generator.next if @generator.next?
-      rescue StopIteration
-      end
-
-      @generator.rewind if Rubinius.ruby18?
-
-      raise StopIteration, "iteration reached end"
-    end
-
     # Rewinds the enumeration sequence by the next method.
     #
     # If the enclosed object responds to a "rewind" method, it is called.

kernel/common/enumerator18.rb

@@ -0,0 +1,37 @@
+module Enumerable
+  class Enumerator
+    # Returns the next object in the enumerator
+    # and move the internal position forward.
+    # When the position reached at the end,
+    # internal position is rewound then StopIteration is raised.
+    #
+    # Note that enumeration sequence by next method
+    # does not affect other non-external enumeration methods,
+    # unless underlying iteration methods itself has side-effect, e.g. IO#each_line.
+    #
+    def next
+      unless @generator
+        # Allow #to_generator to return nil, indicating it has none for
+        # this method.
+        if @object.respond_to? :to_generator
+          @generator = @object.to_generator(@iter)
+        end
+
+        if !@generator and gen = FiberGenerator
+          @generator = gen.new(self)
+        else
+          @generator = ThreadGenerator.new(self, @object, @iter, @args)
+        end
+      end
+
+      begin
+        return @generator.next if @generator.next?
+      rescue StopIteration
+      end
+
+      @generator.rewind
+
+      raise StopIteration, "iteration reached end"
+    end
+  end
+end

kernel/common/enumerator19.rb

@@ -13,6 +13,7 @@ def initialize(obj=undefined, iter=:each, *args, &block)
       @iter = iter.to_sym
       @args = args
       @generator = nil
+      @lookahead = []
     end
 
     def with_index(offset=0)
@@ -31,6 +32,47 @@ def with_index(offset=0)
       end
     end
 
+    # Returns the next object in the enumerator
+    # and move the internal position forward.
+    # When the position reached at the end,
+    # internal position is rewound then StopIteration is raised.
+    #
+    # Note that enumeration sequence by next method
+    # does not affect other non-external enumeration methods,
+    # unless underlying iteration methods itself has side-effect, e.g. IO#each_line.
+    #
+    def next
+      return @lookahead.shift unless @lookahead.empty?
+
+      unless @generator
+        # Allow #to_generator to return nil, indicating it has none for
+        # this method.
+        if @object.respond_to? :to_generator
+          @generator = @object.to_generator(@iter)
+        end
+
+        if !@generator and gen = FiberGenerator
+          @generator = gen.new(self)
+        else
+          @generator = ThreadGenerator.new(self, @object, @iter, @args)
+        end
+      end
+
+      begin
+        return @generator.next if @generator.next?
+      rescue StopIteration
+      end
+
+      raise StopIteration, "iteration reached end"
+    end
+
+    def peek
+      return @lookahead.first unless @lookahead.empty?
+      item = self.next
+      @lookahead << item
+      item
+    end
+
     # A supporting class for Enumerator that allows for easy proxying to a Generator's yield.
     class Yielder
       def initialize(&block)

kernel/common/load_order18.txt

@@ -7,6 +7,7 @@ module18.rbc
 enumerable.rbc
 enumerable18.rbc
 enumerator.rbc
+enumerator18.rbc
 argf.rbc
 argf18.rbc
 tuple.rbc