using a hash as method parameter

options.rb

# Use Hash#assert_valid_keys (from ActiveSupport) to document what
# keys to use when calling the method
def greet(options)
  options.assert_valid_keys(:first_name, :last_name)
  puts "Hello #{options[:first_name]} #{options[:last_name]}!"
end

#=> Hello Thuva Tharma!
greet(:first_name => "Thuva", :last_name => "Tharma")
#=> Unknown key(s): name (ArgumentError)
greet(:name => "Thuva Tharma")

# Do not set the default value for options like below
def greet(options={:first_name => "Thuva", :last_name => "Tharma"})
  puts "Hello #{options[:first_name]} #{options[:last_name]}!"
end

#=> Hello Thuva Tharma!
greet
#=> Hello Thuva ! (Tharma is not used as a default value)
greet(:first_name => "Thuva")

# What you really want is:
def greet(opts={})
  default_options = {
    :first_name => "Thuva",
    :last_name => "Tharma"
  }
  # Note: I'm not altering the value of opts. You should generally
  # not change the value of arguments passed in to the method.
  options = default_options.merge(opts)
  puts "Hello #{options[:first_name]} #{options[:last_name]}!"
end

#=> Hello Thuva Tharma!
greet
#=> Hello Thuva Tharma!
greet(:first_name => "Thuva")

# Throw in Hash#assert_valid_keys in the last method definition
# above and you're golden!