ruby_quiz1.rb

# =============================
# Test case showing what we expect to happen
a1 = 'z'
b1 = 'z'
a = [a1]
b = [b1]

# array '-' https://github.com/ruby/ruby/blob/trunk/array.c#L3806
# It compares elements using their #hash and #eql? methods for efficiency.

# same hashes mean they will be subtracted
a.map(&:hash) # => [1716651113021123031] 
b.map(&:hash) # => [1716651113021123031] 

a1 == b1      # true
a1.eql? b1    # true
a1.equal? b1  # false different object_ids, as expected
a.eql? b      # true

a - b   # = []
b - a   # = []
#EVERYTHING IS GOOD HERE.  DIFFERENT OBJECT_IDS BUT EQUAL OBJECTS SUBTRACT OUT OF ARRAY

# =============================
# Simple class that should act the same as above
class MyObject
  attr_accessor :str
  def initialize(str)
    @str = str
  end

  def eql?(other)
    @str.eql? other.str
  end

  def ==(other)
    @str == other.str
  end
end

# =============================
# Test case that is messed up!
object1 = MyObject.new('z')
object2 = MyObject.new('z')
a = [object1]
b = [object2]

# different hashes mean they will not be subtracted
a.map(&:hash) # => [-3103761982373525360] 
b.map(&:hash) # => [-1675791735293861944] 

object1 == object2      # true
object1.eql? object2    # true
object1.equal? object2  # false different object_ids, as expected
a.eql? b                # true

a - b # = [object1]
b - a # = [object2]

# WHY ARE THESE NOT EMPTY?!?!