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MachineTag is a Ruby library for using machine tags like those used on Flickr and RightScale.


Add this line to your application's Gemfile:

gem 'machine_tag'

And then execute:

$ bundle

Or install it yourself as:

$ gem install machine_tag


MachineTag provides two classes for dealing with machine tags and tags in general: MachineTag::Tag and MachineTag::Set:


The MachineTag::Tag class represents a tag which can either be a machine tag or a plain tag. It inherits from String so it can be used in the same ways.

plain_tag ='geotagged')

plain_tag == 'geotagged'    # => true
plain_tag.machine_tag?      # => false

machine_tag ='geo:lat=34.4348067')

machine_tag == 'geo:lat=34.4348067'     # => true
machine_tag.machine_tag?                # => true
machine_tag.namespace                   # => "geo"
machine_tag.predicate                   # => "lat"
machine_tag.namespace_and_predicate     # => "geo:lat"
machine_tag.value.to_f                  # => 34.4348067

machine_tag = MachineTag::Tag.machine_tag('geo', 'lon', -119.8016962)

machine_tag == 'geo:lon=-119.8016962'   # => true
machine_tag.machine_tag?                # => true


The MachineTag::Set class represents a set of tags and provides a way of looking them up by namespace or by namespace and predicate. It inherits from the Set so it can be used in the same ways. If String objects are passed into it they will automatically be converted to MachineTag::Tag objects.

tags = MachineTag::Set['geotagged', 'geo:lat=34.4348067', 'geo:lon=-119.8016962']

tags.include?('geotagged')  # => true
tags.plain_tags             # => #<Set: {"geotagged"}>
tags.machine_tags           # => #<Set: {"geo:lat=34.4348067", "geo:lon=-119.8016962"}>
tags['geo']                 # => #<Set: {"geo:lat=34.4348067", "geo:lon=-119.8016962"}>
tags['geo:lat']             # => #<Set: {"geo:lat=34.4348067"}>
tags['geo', 'lon']          # => #<Set: {"geo:lon=-119.8016962"}>
tags[/^geo:(lat|lon)$/]     # => #<Set: {"geo:lat=34.4348067", "geo:lon=-119.8016962"}>

More information can be found in the documentation.


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request