[ruby-core:90942] [Ruby trunk Bug#15518] good old Infinite range notation behavior

Issue #15518 has been updated by mrkn (Kenta Murata).


At first, it isn't intentional behavior change. I should fix it, but I need to consider what is the correct behavior.

Ruby 2.5's behavior is given below:

```
$ RBENV_VERSION=2.5 irb --simple-prompt
>> (1 .. 10).first(5)
=> [1, 2, 3, 4, 5]
>> (1 .. 10.0).first(5)
=> [1, 2, 3, 4, 5]
>> (1.0 .. 10).first(5)
Traceback (most recent call last):
        4: from /Users/mrkn/.rbenv/versions/2.5/bin/irb:11:in `<main>'
        3: from (irb):3
        2: from (irb):3:in `first'
        1: from (irb):3:in `each'
TypeError (can't iterate from Float)
>> (1 .. 10r).first(5)
=> [1, 2, 3, 4, 5]
>> (1r .. 10).first(5)
Traceback (most recent call last):
        4: from /Users/mrkn/.rbenv/versions/2.5/bin/irb:11:in `<main>'
        3: from (irb):2
        2: from (irb):2:in `first'
        1: from (irb):2:in `each'
TypeError (can't iterate from Rational)
>> (1 .. 10).step(1).first(5)
=> [1, 2, 3, 4, 5]
>> (1 .. 10.0).step(1).first(5)
=> [1.0, 2.0, 3.0, 4.0, 5.0]
>> (1.0 .. 10).step(1).first(5)
=> [1.0, 2.0, 3.0, 4.0, 5.0]
>> (1 .. 10).step(1.0).first(5)
=> [1.0, 2.0, 3.0, 4.0, 5.0]
>> (1 .. 10r).step(1).first(5)
=> [1, 2, 3, 4, 5]
>> (1r .. 10).step(1).first(5)
=> [(1/1), (2/1), (3/1), (4/1), (5/1)]
>> (1 .. 10).step(1r).first(5)
=> [1, (2/1), (3/1), (4/1), (5/1)]
```

As you can see, the enumerator from Range#step is different from Range#each.
And, on Range#step, the result of the range with float components consists of Float values only while the result of the range with rational components does not.
The reason for this difference is that Range#step has the specialized implementation for the range with float components.

----------------------------------------
Bug #15518: good old Infinite range notation behavior
https://bugs.ruby-lang.org/issues/15518#change-76144

* Author: sakuro (Sakuro OZAWA)
* Status: Assigned
* Priority: Normal
* Assignee: mrkn (Kenta Murata)
* Target version: 
* ruby -v: ruby 2.6.0p0 (2018-12-25 revision 66547) [x86_64-darwin18]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
Ruby 2.5.3's behavior

~~~
# without step, it produces integer sequence
(1..Float::INFINITY).first(10) #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
# with step, it produces floats instead of integers
(1..Float::INFINITY).step(1).first(10) #=> [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0]
~~~

Ruby 2.6.0's behavior

~~~
# endless range
(1..).first(10) #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
# with step, all numbers are integer now
(1..).step(1).first(10) #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# old idiom with Float::INFINITY
(1..Float::INFINITY).first(10) #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
(1..Float::INFINITY).step(1).first(10) #=> FloatDomainError (Infinity)
~~~

Which are intended change and which are not?




-- 
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