Kernel#loop returns the result value of a finished iterator

* vm_eval.c (rb_f_loop): When a loop is stopped by a StopIteration
  exception, return what the enumerator has returned instead of
  nil. [ruby-core:71133] [Feature #11498]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52218 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,9 @@
+Thu Oct 22 18:52:53 2015  Akinori MUSHA  <knu@iDaemons.org>
+
+	* vm_eval.c (rb_f_loop): When a loop is stopped by a StopIteration
+	  exception, return what the enumerator has returned instead of
+	  nil. [ruby-core:71133] [Feature #11498]
+
 Thu Oct 22 18:25:10 2015  Shugo Maeda  <shugo@ruby-lang.org>
 
 	* lib/net/imap (idle): add a new argument timeout for keep-alive.

NEWS

@@ -64,6 +64,11 @@ with all sufficient information, see the ChangeLog file.
     this parameter is bitwise-ORed to oflags generated by normal mode argument.
     [Feature #11253]
 
+* Kernel
+
+  * Kernel#loop, when stopped by a StopIteration exception, returns
+    what the enumerator has returned instead of nil.
+
 * Module
   * Module#deprecate_constant [Feature #11398]
 

test/ruby/test_enumerator.rb

@@ -46,6 +46,14 @@ class TestEnumerator < Test::Unit::TestCase
     }
   end
 
+  def test_loop_return_value
+    assert_equal nil, loop { break }
+    assert_equal 42,  loop { break 42 }
+
+    e = Enumerator.new { |y| y << 1; y << 2; :stopped }
+    assert_equal :stopped, loop { e.next while true }
+  end
+
   def test_nested_iteration
     def (o = Object.new).each
       yield :ok1

vm_eval.c

@@ -24,7 +24,7 @@ static void vm_set_eval_stack(rb_thread_t * th, const rb_iseq_t *iseq, const rb_
 static int vm_collect_local_variables_in_heap(rb_thread_t *th, const VALUE *dfp, const struct local_var_list *vars);
 
 static VALUE rb_eUncaughtThrow;
-static ID id_tag, id_value;
+static ID id_result, id_tag, id_value;
 #define id_mesg idMesg
 
 /* vm_backtrace.c */
@@ -1078,6 +1078,12 @@ loop_i(void)
     return Qnil;
 }
 
+static VALUE
+loop_stop(VALUE dummy, VALUE exc)
+{
+    return rb_attr_get(exc, id_result);
+}
+
 static VALUE
 rb_f_loop_size(VALUE self, VALUE args, VALUE eobj)
 {
@@ -1100,15 +1106,25 @@ rb_f_loop_size(VALUE self, VALUE args, VALUE eobj)
  *       # ...
  *     end
  *
- *  StopIteration raised in the block breaks the loop.
+ *  StopIteration raised in the block breaks the loop.  In this case,
+ *  loop returns the "result" value stored in the exception.
+ *
+ *     enum = Enumerator.new { |y|
+ *       y << "one"
+ *       y << "two"
+ *       :ok
+ *     }
+ *
+ *     result = loop {
+ *       puts enum.next
+ *     } #=> :ok
  */
 
 static VALUE
 rb_f_loop(VALUE self)
 {
     RETURN_SIZED_ENUMERATOR(self, 0, 0, rb_f_loop_size);
-    rb_rescue2(loop_i, (VALUE)0, 0, 0, rb_eStopIteration, (VALUE)0);
+    return rb_rescue2(loop_i, (VALUE)0, loop_stop, (VALUE)0, rb_eStopIteration, (VALUE)0);
-    return Qnil;		/* dummy */
 }
 
 #if VMDEBUG
@@ -2184,6 +2200,7 @@ Init_vm_eval(void)
     rb_define_method(rb_eUncaughtThrow, "value", uncaught_throw_value, 0);
     rb_define_method(rb_eUncaughtThrow, "to_s", uncaught_throw_to_s, 0);
 
+    id_result = rb_intern_const("result");
     id_tag = rb_intern_const("tag");
     id_value = rb_intern_const("value");
 }