Ranges include? or overlap? with Ranges

February 13, 2007 code 2 min read

Update: This has been added to Rails’ active_support.

The past several days I’ve found myself repeatedly writing the following lines to check if two events are conflicting:

window = course.begin_at...course.end_at
window.include?(event.begin_at) || window.include?(event.end_at?)

It finally donned on me that all I’m really doing is checking if two ranges overlap. What I really wanted to be doing is:

  (course.begin_at...course.end_at).overlap?(event.begin_at...event.end_at)

While I was at it, I decided that it only made sense that Range\#include? should be able to take a range:

class Range

  def overlap?(range)
    self.include?(range.first) || range.include?(self.first)
  end

  def include_with_range?(value)
    if value.is_a?(Range)
      last = value.exclude_end? ? value.last - 1 : value.last
      self.include?(value.first) && self.include?(last)
    else
      include_without_range?(value)
    end
  end
  alias_method_chain :include?, :range

end

update: thanks to Daniel Schierbeck for the better implementation of overlap?

So now, I can do things like:

(1..5).include?(2..3)    #=> true
(1..5).include?(4..8)    #=> false
(1..5).overlap?(4..8)    #=> true
(1...5).overlap?(5..10)  #=> false

I love this language!

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