* lib/prime.rb: Have with_index accept an offset parameter.

Based on patch by T Yamada. [#11007]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50854 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Sat Jun 13 00:44:59 2015  Marc-Andre Lafortune  <ruby-core@marc-andre.ca>
+
+	* lib/prime.rb: Have with_index accept an offset parameter.
+	  Based on patch by T Yamada. [#11007]
+
 Fri Jun 12 22:21:12 2015  Kazuhiro NISHIYAMA  <zn@mbf.nifty.com>
 
 	* test/ruby/test_extlibs.rb (TestExtLibs::check_existence): fix

lib/prime.rb

@@ -269,7 +269,15 @@ class Prime
     end
 
     # see +Enumerator+#with_index.
-    alias with_index each_with_index
+    def with_index(offset = 0)
+      return enum_for(:with_index, offset) unless block_given?
+      return each_with_index(&proc) if offset == 0
+
+      each do |prime|
+        yield prime, offset
+        offset += 1
+      end
+    end
 
     # see +Enumerator+#with_object.
     def with_object(obj)

test/test_prime.rb

@@ -86,6 +86,17 @@ class TestPrime < Test::Unit::TestCase
     end
   end
 
+  def test_enumerator_with_index_with_offset
+    enum = Prime.each
+    last = 5-1
+    enum.with_index(5).each do |p,i|
+      break if i >= 100+5
+      assert_equal last+1, i
+      assert_equal PRIMES[i-5], p
+      last = i
+    end
+  end
+
   def test_default_instance_does_not_have_compatibility_methods
     assert !Prime.instance.respond_to?(:succ)
     assert !Prime.instance.respond_to?(:next)