enumerator.c: Introduce Enumerator::ArithmeticSequence

This commit introduces new core class Enumerator::ArithmeticSequence.
Enumerator::ArithmeticSequence is a subclass of Enumerator, and
represents a number generator of an arithmetic sequence.

After this commit, Numeric#step and Range#step without blocks
returned an ArithmeticSequence object instead of an Enumerator.

This class introduces the following incompatibilities:

- You can create a zero-step ArithmeticSequence,
  and its size is not ArgumentError, but Infinity.
- You can create a negative-step ArithmeticSequence from a range.

[ruby-core:82816] [Feature #13904]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64205 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 13 insertions, 5 deletions

diff --git a/range.c b/range.c
index bcc8d1a8f4..56c1ee253b 100644
--- a/range.c
+++ b/range.c
@@ -388,18 +388,26 @@ range_step(int argc, VALUE *argv, VALUE range)
 {
     VALUE b, e, step, tmp;
 
-    RETURN_SIZED_ENUMERATOR(range, argc, argv, range_step_size);
-
     b = RANGE_BEG(range);
     e = RANGE_END(range);
     if (argc == 0) {
-	step = INT2FIX(1);
+        step = INT2FIX(1);
     }
     else {
-	rb_scan_args(argc, argv, "01", &step);
-	step = check_step_domain(step);
+        rb_scan_args(argc, argv, "01", &step);
+    }
+
+    if (!rb_block_given_p()) {
+        if (rb_obj_is_kind_of(b, rb_cNumeric) && (NIL_P(e) || rb_obj_is_kind_of(e, rb_cNumeric))) {
+            return rb_arith_seq_new(range, ID2SYM(rb_frame_this_func()), argc, argv,
+                    range_step_size, b, e, step, EXCL(range));
+        }
+
+        RETURN_SIZED_ENUMERATOR(range, argc, argv, range_step_size);
     }
 
+    step = check_step_domain(step);
+
     if (FIXNUM_P(b) && NIL_P(e) && FIXNUM_P(step)) {
 	long i = FIX2LONG(b), unit = FIX2LONG(step);
 	do {