a.diff

diff --git enumerator.c enumerator.c
index 47a5c7e..2da0b14 100644
--- enumerator.c
+++ enumerator.c
@@ -794,6 +794,26 @@ enumerator_inspect(VALUE obj)
     return rb_exec_recursive(inspect_enumerator, obj, 0);
 }
 
+static VALUE
+enumerator_defer_ii(VALUE i, VALUE y, int c, VALUE *v)
+{
+    return rb_funcall(y, rb_intern("<<"), 1, rb_yield_values2(c, v));
+}
+
+static VALUE
+enumerator_defer_i(VALUE y, VALUE i, int c, VALUE *v)
+{
+    return rb_block_call(i, id_each, 0, 0, enumerator_defer_ii, y);
+}
+
+static VALUE
+enumerator_defer(VALUE obj)
+{
+    VALUE ret = rb_obj_alloc(rb_cEnumerator);
+    rb_block_call(ret, rb_intern("initialize"), 0, 0, enumerator_defer_i, obj);
+    return ret;
+}
+
 /*
  * Yielder
  */
@@ -1099,6 +1119,7 @@ Init_Enumerator(void)
     rb_define_method(rb_cEnumerator, "feed", enumerator_feed, 1);
     rb_define_method(rb_cEnumerator, "rewind", enumerator_rewind, 0);
     rb_define_method(rb_cEnumerator, "inspect", enumerator_inspect, 0);
+    rb_define_method(rb_cEnumerator, "defer", enumerator_defer, 0);
 
     rb_eStopIteration = rb_define_class("StopIteration", rb_eIndexError);
     rb_define_method(rb_eStopIteration, "result", stop_result, 0);

example.rb

a = [1,2,3].map.defer{|x| x*2 }
p a

a.each_with_index do |x,i|
  p [x,i]
end