# Create a structure with a name in Struct
Struct.new("Customer", :name, :address) #=> Struct::Customer
Struct::Customer.new("Dave", "123 Main") #=> #<struct Struct::Customer name="Dave", address="123 Main">
# Create a structure named by its constant
Customer = Struct.new(:name, :address) #=> Customer
Customer.new("Dave", "123 Main") #=> #<struct Customer name="Dave", address="123 Main">
#Array hybrid Hash
require 'set'
s1 = Set.new [1, 2] # -> #<Set: {1, 2}>
s2 = [1, 2].to_set # -> #<Set: {1, 2}>
s1 == s2 # -> true
s1.add("foo") # -> #<Set: {1, 2, "foo"}>
s1.merge([2, 6]) # -> #<Set: {6, 1, 2, "foo"}>
s1.subset? s2 # -> false
s2.subset? s1 # -> true