module Enumerable

def index_with(default = INDEX_WITH_DEFAULT)

# => { title: "hey there", body: "what's up?" }
%i( title body ).index_with { |attr_name| post.public_send(attr_name) }

post = Post.new(title: "hey there", body: "what's up?")

Convert an enumerable to a hash keying it with the enumerable items and with the values returned in the block. 
def index_with(default = INDEX_WITH_DEFAULT)
  if block_given?
    result = {}
    each { |elem| result[elem] = yield(elem) }
    result
  elsif default != INDEX_WITH_DEFAULT
    result = {}
    each { |elem| result[elem] = default }
    result
  else
    to_enum(:index_with) { size if respond_to?(:size) }
  end
end