Tradeoffs

model-view-ideas.rb

class User < Struct.new(:name, :phone, :email)
end

# ---------------------------------------------------------------------------
# Extend on demand
# + no dependency on User class, could be reusable
# + composable
# - cannot unextend user object once extended, but this object could be short
#   lived
# ---------------------------------------------------------------------------

module FormattedPhone
  def phone
    "(%s) %s-%s" % [ super[0,3], super[3,3], super[6,4] ]
  end
end

module FormattedEmail
  def email
    "#{name} <#{super}>"
  end
end

user = User.new "Ben Marini", "4155551212", "ben.marini@example.com"
user.extend FormattedPhone
user.extend FormattedEmail
p user.phone
p user.email

# ---------------------------------------------------------------------------
# Subclass
# - dependency to User class
# - end up with lots of subclasses
# ---------------------------------------------------------------------------

class FormattedUser < User
  def phone
    "(%s) %s-%s" % [ super[0,3], super[3,3], super[6,4] ]
  end

  def email
    "#{name} <#{super}>"
  end
end

user = FormattedUser.new "Ben Marini", "4155551212", "ben.marini@example.com"
p user.phone
p user.email

# ---------------------------------------------------------------------------
# Create a decorator
# - no dependency on User class
# + composable, although composition feels clumsier than the object extension
#   composition
# ---------------------------------------------------------------------------

class PhoneFormatted
  def initialize(source)
    @source = source
  end

  def phone
    "(%s) %s-%s" % [ @source.phone[0,3], @source.phone[3,3], @source.phone[6,4] ]
  end
end

class EmailFormatted
  
end

user = User.new "Ben Marini", "4155551212", "ben.marini@example.com"
user_for_display = PhoneFormatted.new(user)
p user_for_display.phone

# ---------------------------------------------------------------------------
# Create a mix-in
# - creates more methods on User class
# - all user objects will inherit the methods, even if they don't need them
# ---------------------------------------------------------------------------

module PhoneFormatting
  # Assumes super defines phone, a 10 char string of integers
  def formatted_phone
    "(%s) %s-%s" % [ phone[0,3], phone[3,3], phone[6,4] ]
  end
end

class User
  include PhoneFormatting
end

user = User.new "Ben Marini", "4155551212", "ben.marini@example.com"
p user.formatted_phone