enum.rb

def m
  yield :a
end

def n
  yield :a, 1
end

m { |x| p x }
n { |x| p x }

m { |*x| p x }
n { |*x| p x }

p [:a, :b].to_enum.to_a
p [:a, :b].each_with_index.to_a
p [:a, :b].each.to_a
[:a, :b].each_with_index { |x| p x }

gistfile1.txt

sasha:rubinius2.0 brian$ ruby -v enum.rb 
ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-darwin10.7.0]
:a
:a
[:a]
[:a, 1]
[:a, :b]
[[:a, 0], [:b, 1]]
[:a, :b]
:a
:b
sasha:rubinius2.0 brian$ rbx -Xint -X19 -v enum.rb 
rubinius 2.0.0dev (1.9.2 d027e8ae yyyy-mm-dd) [x86_64-apple-darwin10.7.0]
:a
:a
[:a]
[:a, 1]
[:a, :b]
[:a, :b]
[:a, :b]
:a
:b
sasha:rubinius2.0 brian$ rbx -Xint -X19 -v enum.rb 
rubinius 2.0.0dev (1.9.2 d027e8ae yyyy-mm-dd) [x86_64-apple-darwin10.7.0]
:a
:a
[:a]
[:a, 1]
[[:a], [:b]]
[[:a, 0], [:b, 1]]
[[:a], [:b]]
:a
:b
sasha:rubinius2.0 brian$ git diff
diff --git a/kernel/common/enumerable.rb b/kernel/common/enumerable.rb
index eb458e8..9f92734 100644
--- a/kernel/common/enumerable.rb
+++ b/kernel/common/enumerable.rb
@@ -881,7 +881,7 @@ module Enumerable
 
   def to_a(*arg)
     ary = []
-    each(*arg) { |o| ary << o }
+    each(*arg) { |*o| ary << o }
     ary
   end
 
sasha:rubinius2.0 brian$ rbx -Xint -X19 -v enum.rb 
rubinius 2.0.0dev (1.9.2 d027e8ae yyyy-mm-dd) [x86_64-apple-darwin10.7.0]
:a
:a
[:a]
[:a, 1]
[:a, :b]
[[:a, 0], [:b, 1]]
[:a, :b]
[:a, 0]
[:b, 1]
sasha:rubinius2.0 brian$ git diff
diff --git a/kernel/common/enumerable.rb b/kernel/common/enumerable.rb
index eb458e8..3ba9a8c 100644
--- a/kernel/common/enumerable.rb
+++ b/kernel/common/enumerable.rb
@@ -418,7 +418,7 @@ module Enumerable
 
     idx = 0
     each do |o|
-      yield o, idx
+      yield [o, idx]
       idx += 1
     end
 
sasha:rubinius2.0 brian$ rbx -Xint -X19 -v enum.rb 
rubinius 2.0.0dev (1.9.2 d027e8ae yyyy-mm-dd) [x86_64-apple-darwin10.7.0]
:a
:a
[:a]
[:a, 1]
[:a, :b]
[[:a, 0], [:b, 1]]
[:a, :b]
:a
:b
sasha:rubinius2.0 brian$ ruby -v enum.rb 
ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-darwin10.7.0]
:a
:a
[:a]
[:a, 1]
[:a, :b]
[[:a, 0], [:b, 1]]
[:a, :b]
:a
:b
sasha:rubinius2.0 brian$ git diff
diff --git a/kernel/common/enumerable.rb b/kernel/common/enumerable.rb
index eb458e8..513159a 100644
--- a/kernel/common/enumerable.rb
+++ b/kernel/common/enumerable.rb
@@ -881,7 +881,14 @@ module Enumerable
 
   def to_a(*arg)
     ary = []
-    each(*arg) { |o| ary << o }
+    each(*arg) do |a, *b|
+      if b.empty?
+        ary << a
+      else
+        b.unshift a
+        ary << b
+      end
+    end
     ary
   end