From: Thomas Sawyer Date: 2011-11-06T17:26:43+09:00 Subject: [ruby-core:40771] [ruby-trunk - Feature #5534] Redefine Range class and introduce RelativeNumeric and RelativeRange Issue #5534 has been updated by Thomas Sawyer. What is the point of all this? I mean the equality thing is somewhat interesting but how is it really useful? And why does it have any bearing at all on slicing arrays? Really I for one can't make much sense of what you are proposing. ---------------------------------------- Feature #5534: Redefine Range class and introduce RelativeNumeric and RelativeRange http://redmine.ruby-lang.org/issues/5534 Author: Alexey Muranov Status: Open Priority: Normal Assignee: 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://redmine.ruby-lang.org