From: "alexeymuranov (Alexey Muranov)" <redmine@...>
Date: 2012-03-18T22:36:07+09:00
Subject: [ruby-core:43449] [ruby-trunk - Feature #5534] Redefine Range class and introduce RelativeNumeric and RelativeRange


Issue #5534 has been updated by alexeymuranov (Alexey Muranov).


More of my crazy ideas.  Wouldn't it be nice to be able to write:

a, b = 0.5, 10.5
(a..b).each(Integer) do { |n| puts n }
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Feature #5534: Redefine Range class and introduce RelativeNumeric and RelativeRange
https://bugs.ruby-lang.org/issues/5534#change-24916

Author: alexeymuranov (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?



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