Custom comparison operator for difference between arrays in Ruby - ruby

Question

I have two arrays of some class. I want to find the difference between them. But I want it to be based on the value of a specific method call to each instance of this class, instead of the entire instance. Here is some example code where I use Hash for the class.
#!/usr/bin/ruby
require 'awesome_print'
class Hash
def <=> other
puts 'space ship'
self[:a] <=> other[:a]
end
def == other
puts 'double equal'
self[:a] == other[:a]
end
def > other
puts 'greater than'
self[:a] > other[:a]
end
def < other
puts 'less than'
self[:a] < other[:a]
end
def >= other
puts 'greater equal'
self[:a] >= other[:a]
end
def <= other
puts 'less equal'
self[:a] <= other[:a]
end
def eql? other
puts 'eql?'
self[:a].eql? other[:a]
end
def equal? other
puts 'equal?'
self[:a].equal? other[:a]
end
end
c = { a: 1, b: 2, c: 3}
d = { a: 2, b: 3, c: 4}
e1 = { a: 3, b: 4, c: 5}
e2 = { a: 3, b: 4, c: 5}
e3 = { a: 3, b: 5, c: 4}
f1 = { a: 4, b: 5, c: 6}
f2 = { a: 4, b: 5, c: 6}
f3 = { a: 4, b: 6, c: 5}
g = { a: 5, b: 6, c: 7}
h = { a: 6, b: 7, c: 8}
a = [c, d, e1, f1]
b = [e3, f3, g, h]
ap (a - b)
I expect to see 2 elements in the final array, but still seeing 4. Tried overriding all the various comparison operators for the class of each element, Hash in this case, and I can see some calls to the 'double equal', but it still doesn't have the proper effect. What am I doing wrong?

Answer 1

Array#- uses the eql? / hash protocol, just like Hash, Set and Array#uniq:
class Hash
def eql? other
puts 'eql?'
self[:a].eql? other[:a]
end
def hash
puts 'hash'
self[:a].hash
end
end
c = { a: 1, b: 2, c: 3}
d = { a: 2, b: 3, c: 4}
e1 = { a: 3, b: 4, c: 5}
e2 = { a: 3, b: 4, c: 5}
e3 = { a: 3, b: 5, c: 4}
f1 = { a: 4, b: 5, c: 6}
f2 = { a: 4, b: 5, c: 6}
f3 = { a: 4, b: 6, c: 5}
g = { a: 5, b: 6, c: 7}
h = { a: 6, b: 7, c: 8}
a = [c, d, e1, f1]
b = [e3, f3, g, h]
a - b
# => [{a: 1, b: 2, c: 3}, {a: 2, b: 3, c: 4}]