using |= to merge collections into sets is inefficient, the correct way is to use #merge

set.rb

# This shows that set |= collection creates a NEW set with the resulting
# members which is slightly inefficient. #merge does the same thing
# without creating a new Set object

require 'set'

set = Set.new([1,2,3,4])

puts "set is: #{set.inspect} and Object ID before |= is #{set.object_id}"

set |= [4,5,6]

puts "set is: #{set.inspect} and Object ID after |= is #{set.object_id}"

set.merge([6,7,8])

puts "set is: #{set.inspect} and Object ID after merge is #{set.object_id}"

#set is: #<Set: {1, 2, 3, 4}> and Object ID before |= is 2240588820
#set is: #<Set: {5, 6, 1, 2, 3, 4}> and Object ID after |= is 2240588480
#set is: #<Set: {5, 6, 1, 7, 2, 8, 3, 4}> and Object ID after merge is 2240588480