[ruby-core:85780] [Ruby trunk Feature#14473] Add Range#subrange?

Issue #14473 has been updated by owst (Owen Stephens).


Thanks for your thoughts al2o3cr, your "bigger point" is interesting:

> So range_1 claims to be a subset of range_2, but no elements of range_2 are included in range_1.

My thinking here was that the empty set is a subset of all sets, so similar behaviour seemed reasonable for empty/invalid Ranges, i.e. phrase the subset "definition" as: "all elements of range_1 are covered by range_2", which is vacuously true. 

You're right about the implication for `<=` so maybe it's a bad idea to treat "empty"/invalid ranges as if they were empty sets (and thus all equivalent). However, the same thing is true for exclusive/inclusive ranges that contain the same elements (when considered as sets):

~~~ruby
> (1..2).subset?(1...3)
=> true
> (1...3).subset?(1..2)
=> true
> (1..2) == (1...3)
=> false
> Set.new((1..2)) == Set.new((1...3))
=> true
~~~

With `..` vs `...` we can have non-equal Range representations of the same set of elements. I'm not sure what to suggest here. It doesn't quite feel right to restrict `subset?` to only allow an argument with the same `exclude_end?` value.

> min and max also have bad performance characteristics for exclusive ranges that linear_object_p returns false for,

Yes, I didn't like this myself, I'm glad you've brought it up. An option would be to prevent such calls from occurring, which doesn't seem nice, but is probably preferable to performance issues?

----------------------------------------
Feature #14473: Add Range#subrange?
https://bugs.ruby-lang.org/issues/14473#change-70629

* Author: greggzst (Grzegorz Jakubiak)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Hi there,

I'd like to propose a method that returns true when a range that the method gets called on is a subrange of a range passed in as an argument.

Example:

~~~ ruby
(2..4).subrange?(1...4) 
=> true
(-2..2).subrange?(-1..3) 
=> false
~~~




---Files--------------------------------
0001-range.c-add-subset-superset-methods.patch (8.84 KB)
v2-0001-range.c-add-subset-superset-methods.patch (8.85 KB)


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