Lookup Tables With Lambdas

gistfile1.rb

# Adapted from Lookup Tables With Lambdas
# http://www.naildrivin5.com/blog/2012/05/16/lookup-tables-with-lambdas.html

# Lookup with lambdas so we can do a database call or something

CARD_TYPE_COUNTRIES = {
  'discover' => lambda { ['US'] },
  'maestro'  => lambda { ['UK'] },
  'amex'     => lambda { Array.new(1, 'NOWHERE!') }, # Hit database
  'default'  => lambda { ['US','UK','ZA'] }
}

# Try to find the key, if not use the 'default' key
def countries_usable_in(card_type)
  CARD_TYPE_COUNTRIES.fetch(card_type) do
    CARD_TYPE_COUNTRIES['default']
  end.call
end

# Output

> countries_usable_in('discover')
=> ["US"]
> countries_usable_in('amex')
=> ["NOWHERE!"]