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DATA is one of those features one rarely sees in use, but it can be quite handy at times. I used it in rcov to include the xx markup generation library while ensuring the rcov executable remained self-contained (the extension is optional).

I've written a simple FS meant to be used with DATA, in order to structure it into individually accessible files. I then used it to implement a very simplistic pure Ruby compiler (in the sense of composing a .rb file out of many, i.e. a compiler as the very first ones, before the term started to be misused).

A small FS for the DATA section

I could have used minitar to create POSIX tar files in DATA, but I'd have had to implement random access on top of it, so I just defined a feeble YAML-based format:

 #!/usr/bin/env ruby
  
 # ...
 
 # this is the .rb file
 1 + 1
 __END__
 <length of the toc>
 <YAML-serialized toc (obvious from the code)>
 data for all the files in the DataFS
 just one after the other

Creating the FS

The utterly simplistic API for the Writer class is

datafs = DataFS::Writer.new
datafs.add("filename", "file contents")
datafs.add("whatever.rb", "puts 1")
datafs.dump(someIO) # dump to someIO
puts datafs.dump    # just return the serialized representation

The implementation is trivial; an array of FStat objects (holding name, content length and position in the DATA stream) for the embedded files is serialized with YAML and used as the TOC: