Feature #15504

Freeze all Range objects

Added by ko1 (Koichi Sasada) about 2 years ago. Updated 4 months ago.

Target version:



Range is currently non-frozen. How about freezing all Range objects?


We froze some types of objects: Numerics (r47523) and Symbols [Feature #8906]. I believe that making objects immutable solves some kinds of programming difficulties.

Range is mutable at least when written as Range literal. So we can write the following weird program:

  r = (1..3)
  p r.instance_variable_get(:@foo)
  #=> 1st time: nil
  #=> 2nd time: :bar
  r.instance_variable_set(:@foo, :bar)

In range.c, there is a comment (thanks znz-san):

static void
range_modify(VALUE range)
    /* Ranges are immutable, so that they should be initialized only once. */
    if (RANGE_EXCL(range) != Qnil) {
    rb_name_err_raise("`initialize' called twice", range, ID2SYM(idInitialize));


Index: range.c
--- range.c (リビジョン 66699)
+++ range.c (作業コピー)
@@ -45,6 +45,8 @@
     RANGE_SET_EXCL(range, exclude_end);
     RANGE_SET_BEG(range, beg);
     RANGE_SET_END(range, end);
+    rb_obj_freeze(range);



There are several usages of mutable Range in the tests.

  • (1) Taint-flag
  • (2) Add singleton methods.
  • (3) Subclass with mutable states

Maybe (2) and (3) are crucial.


Related issues

Related to Ruby master - Feature #17195: Freeze Enumerator::ArithmeticSequence objectsRejectedActions

Updated by marcandre (Marc-Andre Lafortune) about 2 years ago

I think that (2) and (3) are indeed capital points. Freezing range litterals (only) might be a better idea? with an approach like frozen string literals?

Not that even frozen ranges aren't completely immutable:

r = ('a'..'z').freeze
r # => "a".."Z" 

Updated by Eregon (Benoit Daloze) over 1 year ago

I think it would make sense to freeze Range literals.

Adding methods to Range might be reasonable, but singleton methods, I would think much less so.

Updated by mame (Yusuke Endoh) over 1 year ago

I guess Eregon (Benoit Daloze) came from #15950. Will ary[-3..] be as efficient as ary[-3, 3] by freezing and deduping a literal (-3..)? Looks good if we can confirm it by an experiment.

Some thoughts:

  • Even if a range is frozen, ("a".."z") should not be deduped because of the reason marcandre (Marc-Andre Lafortune) said.
  • I'm for freezing all Ranges, not only Range literals. I hate the idea of freezing only literals because casually mixing frozen and unfrozen objects leads to hard-to-debug bugs that depend upon data flow.
  • It would be the most elegant if the combination of MJIT and escape analysis solves this kind of performance problems.

Updated by ko1 (Koichi Sasada) 6 months ago

I got an issue on Ractor.

def test

r1 = test do
  r2 = test
  • compiler cached Range (1..2) because they begin and end are frozen literals. The test method returns a cached same range object.
  • it means test returns not-immutable but same object. It violate the Ractor's memory model.

To solve it, there are two options.

(1) avoid cache at compile time.
(2) freeze Range objects which will be cached by th compiler.

For performance reason, I want to choose (2).

After that, could you please discuss all Range objects should be frozen or not.



Updated by sawa (Tsuyoshi Sawada) 6 months ago

  • Description updated (diff)
  • Subject changed from Freeze all Range object to Freeze all Range objects

Updated by Eregon (Benoit Daloze) 6 months ago

Right, every object cached at parse time must be deeply immutable, I would think that was an oversight.

Updated by matz (Yukihiro Matsumoto) 4 months ago

I agree with making ranges frozen. I don't see any particular case that could be broken by frozen ranges.
Since there's possiblity of breakage, I'd like to experiment it.


Updated by ko1 (Koichi Sasada) 4 months ago

Ok, I freeze all Ranges except sub-classes.


Updated by ko1 (Koichi Sasada) 4 months ago

  • Status changed from Open to Closed

Applied in changeset git|0096d2b895395df5ab8696d3b6d444dc1b7730b6.

freeze all Range objects.

Matz want to try to freeze all Range objects.
[Feature #15504]

Updated by Eregon (Benoit Daloze) 4 months ago


Related, should Enumerator::ArithmeticSequence be frozen too?

Updated by ko1 (Koichi Sasada) 4 months ago

Eregon (Benoit Daloze) wrote in #note-10:

Related, should Enumerator::ArithmeticSequence be frozen too?

new ticket?


Updated by Eregon (Benoit Daloze) 4 months ago

  • Related to Feature #17195: Freeze Enumerator::ArithmeticSequence objects added

Updated by Eregon (Benoit Daloze) 4 months ago

ko1 (Koichi Sasada) wrote in #note-11:

Eregon (Benoit Daloze) wrote in #note-10:

Related, should Enumerator::ArithmeticSequence be frozen too?

new ticket?

I filed #17195

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