* enumerator.c (rb_eStopIteration), eval.c (rb_f_loop), ruby.h:

  Add a new exception class StopIteration, which breaks Kernel#loop
  iteration when raised; backported from 1.9.

* enumerator.c (enumerator_next, enumerator_rewind): Implement
  #next and #rewind using the "generator" library.

* lib/generator.rb: Implement Enumerable::Enumerator#next and
  #rewind.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@15954 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 38 insertions, 0 deletions

diff --git a/lib/generator.rb b/lib/generator.rb
index a010559b60..dbdd0f40a9 100644
--- a/lib/generator.rb
+++ b/lib/generator.rb
@@ -165,6 +165,44 @@ class Generator
   end
 end
 
+class Enumerable::Enumerator
+  def __generator
+    @generator ||= Generator.new(self)
+  end
+  private :__generator
+
+  # call-seq:
+  #   e.next   => object
+  #
+  # Returns the next object in the enumerator, and move the internal
+  # position forward.  When the position reached at the end, internal
+  # position is rewinded 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.
+  #
+  # Caution: This feature internally uses Generator, which uses callcc
+  # to stop and resume enumeration to fetch each value.  Use with care
+  # and be aware of the performance loss.
+  def next
+    g = __generator
+    return g.next unless g.end?
+
+    g.rewind
+    raise StopIteration, 'iteration reached at end' 
+  end
+
+  # call-seq:
+  #   e.rewind   => e
+  #
+  # Rewinds the enumeration sequence by the next method.
+  def rewind
+    __generator.rewind
+    self
+  end
+end
+
 #
 # SyncEnumerator creates an Enumerable object from multiple Enumerable
 # objects and enumerates them synchronously.