From: "akr (Akira Tanaka) via ruby-core" <ruby-core@...>
Date: 2023-09-18T13:55:02+00:00
Subject: [ruby-core:114800] [Ruby master Feature#19839] Need a method to check if two ranges overlap

Issue #19839 has been updated by akr (Akira Tanaka).


I found another corner case.

```
% ./ruby -e 'r = (...-Float::INFINITY); p r.overlap?(r)' 
true
% ./ruby -e 'r = (...[]); p r.overlap?(r)'
true
% ./ruby -e 'r = (...""); p r.overlap?(r)' 
true
% ./ruby -e 'r = (...true); p r.overlap?(r)'
true
% ./ruby -e 'r = (...false); p r.overlap?(r)'
true
% ./ruby -e 'r = (...Object.new); p r.overlap?(r)'
true
% ./ruby -v
ruby 3.3.0dev (2023-09-16T22:27:04Z master cd67c0d204) [x86_64-linux]
```

They are `(...MINIMUM)` where MINIMUM is a value that there is no value less than that.

`(...MINIMUM)` is empty because
(1) it doesn't contain MINIMUM itself because `...` is used (exclude_end is true) and
(2) it doesn't contain other values because there is no value less than MINIMUM.

But `(...MINIMUM).overlap?(...MINIMUM)` returns true as shown above.
It means Ruby says there is a value contained in (...MINIMUM).
It is invalid.

Note that true, false, and `Object.new` has `<=>` method defined by Kernel.
It determines self is equal to itself and other objects are not comparable.
Thus, they can be considered as minimum values (and maximum values).

I think this problem is difficult to solve.
We have no clean way to detect minimum values.

Some options:
(1) introduce some protocol to detect minimum values such as `minimum?` method.
(2) hard code minimum values of builtin classes in `Range#overlap?` and use `minimum?` for user-defined classes. 
(3) document this limitation.







----------------------------------------
Feature #19839: Need a method to check if two ranges overlap
https://bugs.ruby-lang.org/issues/19839#change-104645

* Author: shouichi (Shouichi Kamiya)
* Status: Closed
* Priority: Normal
----------------------------------------
It would be convenient to have a method that checks if two ranges overlap. For example,

```
(0..10).overlap?(5..15) #=> true
(0..10).overlap?(20..30) #=> false
```



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