[ruby-core:115031] [Ruby master Misc#18984] Doc for Range#size for Float/Rational does not make sense

Issue #18984 has been updated by mame (Yusuke Endoh).


Discussed at the dev meeting. @matz 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.

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

----------------------------------------
Misc #18984: Doc for Range#size for Float/Rational does not make sense
https://bugs.ruby-lang.org/issues/18984#change-104902

* Author: masasakano (Masa Sakano)
* Status: Open
* Priority: Normal
----------------------------------------
When `Range` consists of any Numeric, according to [Official docs for Ruby-3.1.2](https://ruby-doc.org/core-3.1.2/Range.html#method-i-size), `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":

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

Yet, `Range#size` of such Ranges returns an Integer

```ruby
(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](https://ruby-doc.org/core-3.1.2/Range.html#method-i-size), avoiding the confusing expression "the count of elements", because "elements" are not unambiguously defined for Range of Float/Rational.




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