[LRUG] Comparable Null Objects

Frederick Cheung frederick.cheung at gmail.com
Wed Jul 15 05:17:02 PDT 2015

On 15 July 2015 at 13:03:21, Duncan Stuart (dgmstuart at gmail.com) wrote:

$ NoExpectedDate.new > Date.today
=> true

$ Date.today > NoExpectedDate.new
ArgumentError: comparison of Date with NoExpectedDate failed

I think this is because Date's <=> method expects it's argument to be a Date object or a number ("a numeric value as an astronomical Julian day number"). I've tried defining to_i and to_r on NoExpectedDate, but no dice.

Can I get NoExpectedDate to pretend to be a Date (like SimpleDelegator lies about it's class)? Is that evil?

I think this is what coercion is for (e.g. http://www.mutuallyhuman.com/blog/2011/01/25/class-coercion-in-ruby/ )


I suppose I could always just define a method on Event to do this particular sort, but that seems nasty for all sorts of reasons:

def sort_by_expected_date sort do |a, b| 

    if b.class = NoExpectedDate 



      a <=> b




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