Mash – Mocking Hash for total poser objects

Note: Development of Mash has now moved to Hashie, a generic Hash toolkit.

There are a number of times when I need something like an OpenStruct with a little more power. Often times this is for API-esque calls that don’t merit a full on ActiveResource. I wrote a small class for use with my ruby-github library and wanted to make it a separate gem because I think it’s pretty useful to have around.


Basically a Mash is a Hash that acts a little more like a full-fledged object when it comes to the keyed values. Using Ruby’s method punctuation idioms, you can easily create pseudo-objects that store information in a clean, easy way. At a basic level this just means writing and reading arbitrary attributes, like so:

author = # => nil = "Michael Bleigh" # => "Michael Bleigh" = "" author.inspect # => <Mock name="Michael Bleigh" email="">

So far that’s pretty much how an OpenStruct behaves. And, like an OpenStruct, you can pass in a hash and it will convert it. Unlike an OpenStruct, however, Mash will recursively descend, converting Hashes into Mashes so you can assign multiple levels from a single source hash. Take this as an example:

hash = { :author => {:name => "Michael Bleigh", :email => ""},        :gems => [{:name => "ruby-github", :id => 1}, {:name => "mash", :id => 2}]}  mash = # => "Michael Bleigh" # => "ruby-github"

This can be really useful if you have just parsed out XML or JSON into a hash and just want to dump it into a richer format. It’s just that easy! You can use the ? operator at the end to check for whether or not an attribute has already been assigned:

mash = # => false = "Michael Bleigh" # => true

A final, and a little more difficult to understand, method modifier is a bang (!) at the end of the method. This essentially forces the Mash to initialize that value as a Mash if it isn’t already initialized (it will return the existing value if one does exist). Using this method, you can set ‘deep’ values without the hassle of going through many lines of code. Example:

mash =!.name = "Michael Bleigh"!.url = "" mash.inspect # => <Mash author=<Mash name="Michael Bleigh" info=<Mash url="">>> # => ""

One final useful way to use the Mash library is by extending it! Subclassing Mash can give you some nice easy ways to create simple record-like objects:

class Person < Mash   def full_name     "#{first_name}#{" " if first_name? && last_name?}#{last_name}"   end end  bob = => "Bob", :last_name => "Bobson") bob.full_name # => "Michael Bleigh"

For advanced usage that I’m not quite ready to tackle in a blog post, you can override assignment methods (such as name= and this behavior will be picked up even when the Mash is being initialized by cloning a Hash.


It’s available as a gem on Rubyforge, so your easiest method will be:

sudo gem install mash

If you prefer to clone the GitHub source directly:

git clone git://

This is all very simple but also very powerful. I have a number of projects that will be getting some Mashes now that I’ve written the library, and maybe you’ll find a use for it as well.