Bug #16165
closed
Endless ranges have inconsistency between #cover? and #include?
Description
In an endless Range, I'd expect to be able to use #include? just as I do with a Range that has an end value. It would amount to just a check on whether the argument was greater than or equal to the start value of that Range (and likewise, if "startless" ranges are eventually supported, it'd just be a check on the Range's end value, or if it were possibly to have both a startless and endless Range, always return true).
In Ruby 2.6.4, behaviour is unexpected. I "need to know" if a Range is endless and implement the check myself, because using #include? results in RangeError (cannot get the last element of endless range). The reason this feels like a bug, apart from being merely unhelpful, is because #cover? accepts a single value rather than a Range too - and this behaves exactly as we might expect. I can ask if (1..).cover?(0) and get false, or (1..).cover?(2000) and get true, just like I'd expect.
It's weird that #cover? works, but #include? throws an unusual exception. In my particular use case I have an array of Ranges for various periods of time that typically terminates in an endless Range for "everything afterwards". Being able to write clear, simple code that treats each of these the same to see if a given discrete time falls into a particular time "bucket" is obviously valuable. It'd be ugly to have to check each time to see if a given Range was endless and treat it specially, just because #include? would otherwise raise an exception. In this case, at least, #cover? comes to the rescue :-)
If there's a general agreement that this should be a thing, I could look into producing a patch to have #include? be a bit better behaved when dealing with endless ranges.
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