Organizing constants in Ruby using class methods

We were recently discussing how to organize a collection of constant values in a Ruby/Rails app. A lot of people tend to instinctively choose CONSTANTS for this use, but they can be hard to organize, hard to test, and harder to read.

class Foo
  BAZ = [["baz", "qux"], ["panda", "bamboo"]]
end

puts Foo::BAZ.inspect # => [["baz", "qux"], ["panda", "bamboo"]]

Instead, consider class methods that return constant values like so:

class Foo
  def self.bar
    %w(baz qux)
  end

  def self.foo
    %w(panda bamboo)
  end

  BAZ = [bar, foo]
end

puts Foo::BAZ.inspect # => [["baz", "qux"], ["panda", "bamboo"]]

That allows composure of values with some extra organization, which is handy if you need to keep a certan named constant around (Foo::BAZ in this case).

Of course, you could only use class methods:

class Foo
  def self.bar
    %w(baz qux)
  end

  def self.foo
    %w(panda bamboo)
  end

  def self.baz
    [bar, foo]
  end
end

puts Foo.baz.inspect # => [["baz", "qux"], ["panda", "bamboo"]]

That approach has an added benefit of being easier to refactor and test as use cases change. Unlike CONSTANTS, you could add optional parameters, etc as the need comes up.