[ruby-core:102563] [Ruby master Misc#17637] Endless ranges with `nil` boundary weird behavior

Issue #17637 has been updated by mame (Yusuke Endoh).


Hi, I proposed and implemented a endless range.

This is a trade-off between early failure and usability/consistency.
While the feature is indeed error-prone in some cases, it is more consistent and useful.

It is possible to allow only `(1..)` and deny `(1..nil)`.
In fact, `(1..nil)` used to raise an exception for a short period of development phase of Ruby 2.6.

https://github.com/ruby/ruby/commit/48de2ea5f9b9067779acb0f7f76e5f879f2b42c0

But, to create a conditionally endless range, we need to write `max ? (1..max) : (1..)` or `Range.new(1, max)` if `(1..nil)` is prohibited.
The current behavior allows to just write `(1..max)`. Thus, it was reverted.

It is very difficult to change the behavior from now because of the compatibility issue.
But as I recall, this is the third time for me to see this issue reported.
(The first is #14845. I couldn't find the second but I think someone said it in GitHub comments or else.)
If it is a major source of bugs, and if a conditionally endless range is very rare, I'm personally open for the change.

----------------------------------------
Misc #17637: Endless ranges with `nil` boundary weird behavior
https://bugs.ruby-lang.org/issues/17637#change-90465

* Author: gud (gud gud)
* Status: Open
* Priority: Normal
----------------------------------------

Basically it's about this https://andycroll.com/ruby/watch-out-for-nils-in-ranges/

Since Ruby 2.6 we have this weird syntax (0..nil) which is really really bug prone

e.g. we have dynamic upper boundary like

```
lower = 0
upper = some_method(arg1, arg2)

(lower..upper).each do { |s| some_method2(s) }
```

We rarely do `nil` checks in Ruby so it's really easy to have Infinity loop in the end.
Previous Argument error was more intuitive since it throws exception instead of silently looping forever.

+ some additional strange behavior:

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

(0..Float::INFINITY).count
=> hangs, I guess same infinity loop
```

Having explicit parameter `Float::INFINITY` (as in previous versions) looks more like a proper design instead of allowing `nil` as a valid parameter.

You may think of it as **I would like to have a range from 0 to nothing, what is it actually ?**
And I guess the answer is **Nothing**.
Fixing `(0..Float::INFINITY).count` this case it also important I believe.

Tested on `ruby 2.7.1p83`



-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:[e-mail]?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>