struct.rb

def reset
  Object.send :remove_const, 'Person'
end

# Inheriting from struct
class Person < Struct.new(:first_name, :last_name)
  def full_name
    [first_name, last_name].compact.join(' ')
  end
end

Person.ancestors # => [Person, #<Class:0x007fa2cb8c8230>, Struct, Enumerable, Object, Kernel, BasicObject]
justin = Person.new("Justin", "Campbell") # => #<struct Person first_name="Justin", last_name="Campbell">
justin.full_name # => "Justin Campbell"

reset

# Struct with block
Person = Struct.new(:first_name, :last_name) do
  def full_name
    [first_name, last_name].compact.join(' ')
  end
end

Person.ancestors # => [Person, Struct, Enumerable, Object, Kernel, BasicObject]
justin = Person.new("Justin", "Campbell") # => #<struct Person first_name="Justin", last_name="Campbell">
justin.full_name # => "Justin Campbell"

reset

# Class with attr_accessor (equivalent to Struct)
class Person
  attr_accessor :first_name, :last_name

  def initialize(first_name, last_name)
    self.first_name = first_name
    self.last_name = last_name
  end

  def full_name
    [first_name, last_name].compact.join(' ')
  end
end

Person.ancestors # => [Person, Object, Kernel, BasicObject]
justin = Person.new("Justin", "Campbell") # => #<Person:0x007fa2cb8c62c8 @first_name="Justin", @last_name="Campbell">
justin.full_name # => "Justin Campbell"

reset

# Class with attr_reader (immutable)
class Person
  attr_reader :first_name, :last_name

  def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
  end

  def full_name
    [first_name, last_name].compact.join(' ')
  end
end

Person.ancestors # => [Person, Object, Kernel, BasicObject]
justin = Person.new("Justin", "Campbell") # => #<Person:0x007fa2cb8c5828 @first_name="Justin", @last_name="Campbell">
justin.full_name # => "Justin Campbell"