At one point a while back, I had a config file outside a rails app and what I wanted was something like this:

Given this mappping definition /order/:meal/:cheese How can I turn these strings into parsed hashes? /order/hotdog/cheddar -> {meal:'hotdog', cheese:'cheddar'}

I knew that something in Rails was doing this. I just didn’t know what. I also didn’t know what assumptions or abstraction level it was working at.

Journey into Journey

The gem that handles parsing the routes file and creating a tree is journey. Journey used to be (years ago) a separate gem but is not integrated into action_dispatch which itself is a part of actionpack. So to install it you need to gem install actionpack (or use bundler) but to include it in your program you need to require 'action_dispatch/journey'. If you have any rails 4+ gem installed on your system, you don’t need to install anything. Action pack comes with rails.

require 'action_dispatch/journey'

# reorganize pattern matches into hashes
def hashify_match matches
  h = {}
  matches.names.each_with_index do |key, i|
    h[key.to_sym] = matches.captures[i]

pattern = ActionDispatch::Journey::Path::Pattern.from_string '/order/(:meal(/:cheese))'
matches = pattern.match '/order/hamburger/american'
puts hashify_match matches

matches = pattern.match '/order/hotdog/cheddar'
puts hashify_match matches

# {:meal=>"hamburger", :cheese=>"american"}
# {:meal=>"hotdog", :cheese=>"cheddar"}

We have to have hashify_match reorganize our objects because this is what pattern.match returns:

irb(main):001:0> matches = pattern.match '/order/hamburger/american'
=> #<ActionDispatch::Journey::Path::Pattern::MatchData:0x007f9d4d527aa0
 @match=#<MatchData "/order/hamburger/american" 1:"hamburger" 2:"american">,
 @names=["meal", "cheese"],
 @offsets=[0, 0, 0]>

So we have to turn these ordered matches into a hash.

irb(main):001:0> matches.names
=> ["meal", "cheese"]

irb(main):002:0> matches.captures
=> ["hamburger", "american"]

We could also zip the results together but we wouldn’t have symbolized keys.

irb(main):001:0> Hash[]
=> {"meal"=>"hamburger", "cheese"=>"american"}

You could symbolize them easily within a rails app or by including active support.

require 'active_support'
require 'active_support/core_ext'