Maintaining keyword arity is hard

You know, sometimes you just can't bother with explicitly stating what keyword arguments that you want to pass.

	def address_method(city: "Bloomington", state: "IN", street: "123 fake st")
	print x,y,z,"\n"
	end
	input = {city: "Indianapolis", street: "321 faux st", zip: "12345"}
	address_method(input_address) # => ArgumentError: unknown keyword: zip
	addr_mthd = method(:address_method)
	acceptable_keywords = addr_mthd.parameters.select{|p| p[0] == :key}.map(&:last)
	accepted_input = input.select{|(k,v)| acceptable_keywords.include?(k)}
	address_method(accepted_input) # => IndianapolisIN321 faux st

view raw keyword_arg_arity.rb hosted with ❤ by GitHub

DRY up your class definitions

Have you ever felt vaguely annoyed at typing the class name in the file name and then typing it again inside the file as well? Have you ever changed a class name and forgotten to change the file name?

Well I have good news for you!

	# app/models/user.rb
	Dryer.def_class(__FILE__) do
	def hi
	"hello world"
	end
	end
	User.new.hi
	=> "hello world"
	# app/models/instruments/horn.rb
	Dryer.def_class(__FILE__) do
	def play
	"toot!"
	end
	end
	Instruments::Horn.new.play
	=> "toot!"
	# app/models/address.rb
	Dryer.def_class(__FILE__, ActiveRecord::Base) do
	end
	Address.new.respond_to? :save
	=> true

view raw dryer_examples.rb hosted with ❤ by GitHub

Here is the code! This class allows you to condsolidate the declaration of class names into the file name. It also handles namespacing based on the file path if you are using Rails autoloading.

This works with the single exception of constant lookup via nesting, so you will need to replace constants with variables and methods.

	class Dryer = Struct.new(:file_path, :super_class, :blk) do
	def self.def_class(file_path, super_class=Object, &blk)
	new(file_path, super_class, blk).def_class
	end
	def def_class
	constant_names.each.with_index.inject(Object) do |const, (next_const, index)|
	if constant_names.length == index + 1
	# this is needed to set the class name so that activerecord
	# works properly.
	klass = const.const_set(next_const, Class.new(super_class))
	# here we eval the class block to define methods and everything
	klass.class_eval &blk
	else
	const.const_get(next_const)
	end
	end
	end
	def constant_names
	get_namespaces.split('/').map(&:camelcase)
	end
	def get_namespaces
	# this assumes you are following ruby convention of paths corresponding to
	# namespaces. If you do not, this can't work.
	file_path.gsub(most_likely_relative_path, '').gsub(".rb", '')
	end
	def most_likely_relative_path
	# sort by length selects the path closest to the original file path.
	possible_relative_paths.sort_by(&:length).last + '/'
	end
	def possible_relative_paths
	$LOAD_PATH.select{|p| file_path[/^#{p}/]}
	end
	end

view raw dryer_code.rb hosted with ❤ by GitHub

How to reverse an array in Ruby in O(1)

class ReverseArray < Struct.new(:array)
  include Enumerable
  def each(&blk)
    i = array.length - 1
    while i >= 0 do
      yield array[i]
      i -= 1
    end 
  end
end

array = (0..10000).to_a
reverse_array = ReverseArray.new(array)

array.last == reverse_array.first
=> true