[ruby-core:50791] [ruby-trunk - Feature #7545] Make Range act as a "lazy ordered set"

Issue #7545 has been updated by phluid61 (Matthew Kerwin).


alexeymuranov (Alexey Muranov) wrote:
> But it is not a set, it seems to be just a pair of bounds, like a 2-element array. I propose to change the semantics, and hence behavior in applications like `Array#slice`.

You say that "[range] is not a set" but you propose making it one?  Why not instead create a class (e.g. LazyBoundedSet, which may or may not be backed by a Range at your discretion) which explicitly *is* a set, and doesn't require breaking existing functionality, let alone breaking Rubyists' current understanding?

> For the equality of 1...1 and 3...3, i meant that they both model the same object: the empty set, this was the actual reason.

Point in case: they model the same (empty) _set_, but they are different _ranges_.
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Feature #7545: Make Range act as a "lazy ordered set"
https://bugs.ruby-lang.org/issues/7545#change-34637

Author: alexeymuranov (Alexey Muranov)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: Next Major


=begin
# Make Range act as a "lazy ordered set"

This replaces my older feature request #5534.

I propose the following new behavior of (({Range})):

  (1..3).to_a               # => [1, 2, 3]
  (3..1).to_a               # => [3, 2, 1]
  'a'..'c'.to_a             # => ['a', 'b', 'c']
  'c'..'a'.to_a             # => ['c', 'b', 'a']
  1...1 == 3...3            # => true
  1...1 == 'a'...'a'        # => true
  1...1 == Range::EMPTY_SET # => true
  1..2 == 1...3             # => false
  1...3.include?(2.5)       # => true

Also, maybe in the future the following behavior can be possible:

  r1 = Range.new('a', 'bc', :deglex)
  r1.include?('abc') # => false
  r1.to_a            # => ['a', 'b', ..., 'az', 'ba', 'bb', 'bc']
  r2 = Range.new('a', 'bc', :lex)
  r2.include?('abc') # => true
  r2.to_a            # => Error

and this:

  ((0.5)..(5.5)).to_a(Integer) # => [1, 2, 3, 4, 5]
  ((0.5)..(5.5)).each(Integer) do |i| puts i end

(i imagine this would require additions to the (({Integer})) class, so that it
know more about "real" ranges).


=end



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