From: "mame (Yusuke Endoh)" Date: 2012-03-27T22:54:17+09:00 Subject: [ruby-core:43738] [ruby-trunk - Feature #5534][Assigned] Redefine Range class and introduce RelativeNumeric and RelativeRange Issue #5534 has been updated by mame (Yusuke Endoh). Status changed from Open to Assigned Assignee set to matz (Yukihiro Matsumoto) ---------------------------------------- Feature #5534: Redefine Range class and introduce RelativeNumeric and RelativeRange https://bugs.ruby-lang.org/issues/5534#change-25244 Author: alexeymuranov (Alexey Muranov) Status: Assigned Priority: Normal Assignee: matz (Yukihiro Matsumoto) Category: core Target version: I started by commenting on Feature #4541, but ended up with proposing a new feature myself. I suggest to redefine the behavior of Range class so that all empty ranges be equal: (2..1) == (1..-1) and (2..1) == (1...1) and (2..1) == ('z'..'a') # => true In other fords, ranges `r1` and `r2` should be equal if and only if `r1.include?` and `r2.include?` give identical results for all inputs. (Why is it not `includes?` by the way?) Thus Range would simply be a way to store certain infinite sets. This change will result in not being able to slice an array `a` from beginning and from the end simultaneously with `a[1..-2]`. To resolve this, i propose to introduce `RelativeNumeric` and `RelativeRange` classes. Each `RelativeNumeric` would be a `Numeric` with an "anchor", which is an arbitrary symbol. For example: 3.from(:bottom) # would return a "relative" 3 with "anchor" :bottom One can define shortcuts `#from_bottom` for `#from(:bottom)` and `#from_top` for `#from_top`. A `RelativeRange` is a range with relative bounds. If bounds of a relative range r are relative to the same anchor and the range is seen to be empty, it should be equal to *the* empty relative range with this anchor. For example: (3.from(:center)..2.from(:center)) == (0.from(:center)...0.from(:center)) # => true Now, to do what is currently done by `a[1..-2]`, one can redefine `Array#slice` to use instead: a[1.from_bottom..(-1).from_top] What do you think? -- http://bugs.ruby-lang.org/