Misc #18984: Doc for Range#size for Float/Rational does not make sense

• Status: Closed
• Assignee: -

[masasakano (Masa Sakano)]

When Range consists of any Numeric, according to Official docs for Ruby-3.1.2, Range#size should,

Returns the count of elements in self if both begin and end values are numeric;

Indeed, when Range consists of only Integer, this makes sense.
However, when the begin value of Range is a Float or Rational, "the count of elements" does not make sense. Such Ranges are not iteratable, suggesting there are no such things as "elements":

(0.51..5.quo(2)).each{}  # => TypeError

Yet, Range#size of such Ranges returns an Integer

(0.51..5.quo(2)).size  # => 2

It seems both begin and end values of a Range are rounded (Numeric#round) to the nearest Integer before Range#size is calculated.

If this is the specification, I suggest it should be clearly stated in the Official docs, avoiding the confusing expression "the count of elements", because "elements" are not unambiguously defined for Range of Float/Rational.

[Eregon (Benoit Daloze)]

• Assignee deleted (core)

[Eregon (Benoit Daloze)]

Please do not assign ruby-core, that sends too many emails.

[sawa (Tsuyoshi Sawada)]

I think this is a bug. Since (0.51..5.quo(2)).count raises a TypeError and (0.51..5.quo(2)).size is supposed to follow that, it should raise a TypeError as well.

[kyanagi (Kouhei Yanagita)]

It seems that there is a similar issue with beginless ranges.

(..0).size # => Infinity
(..0).count # => Infinity
(..0).each {} # => can't iterate from NilClass (TypeError)

Is it reasonable to say the size is infinite even if it can't be iterated?

[mame (Yusuke Endoh)]

Discussed at the dev meeting. @matz (Yukihiro Matsumoto) said that he wanted to try to fix the behavior of Range#size instead of changing the document. If the incompatibilty is found significant, it will be reconsidered.

(0.51..5.quo(2)).size #=> TypeError
(..0).size            #=> TypeError

[kyanagi (Kouhei Yanagita)]

I created a PR: https://github.com/ruby/ruby/pull/8663

What should we do about Range#count?

(..0).count # => Infinity
(nil..nil).count # => Infinity

[kyanagi (Kouhei Yanagita)]

• Status changed from Open to Closed

Applied in changeset git|9f6deaa6888a423720b4b127b5314f0ad26cc2e6.

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[Misc #18984] Raise TypeError from Range#size if the range is not iterable