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The code from Russ Olsen's book Design Patterns in Ruby (
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Latest commit 9d0ee2c @russolsen Text now makes sense


The code from Russ Olsen's book Design Patterns in Ruby (

I've updated the code so that it runs with Ruby 2.2.1 but do keep in mind that some of this code is now nine years old: Thinking and coding styles do change.

The repo is organized by chapter, one subdirectory per chapter. In each subdirectory you will find Ruby files with names like ex1_report.rb or ex15_subclass_test.rb or ex13_account_demo.rb.

The files are numbered to roughly follow the order that the code appears in the book. For example, chap01/ex3_vehicle.rb appears in the book before chap01/ex8_delegate.rb.

The files whose names end with “demo” are a bit special. These guys contain the code for the fragmentary, inline examples (as opposed to full classes) that are sprinkled throughout the book – take a look at the code on page 6. These “demo” files actually make use of a couple of utility methods found in the "example.rb" in the root code directory.

The problem I had with fragmentary examples was that I wanted to be sure that the code actually worked, and that the output that I claimed the code produced actually came out of the code, no small feat when you are dealing with more than 100 separate examples. The solution that I came up with was to wrap each little example in a call to a method (defined in example.rb) called example:

example %q{
my_car =

Look closely at the code above and you will see that the example code gets passed to the example method as a string. The example method does two things with that string: first it prints it out (so that I could snag the code for inclusion in the book) and then executes it (so that I could snag the output for inclusion in the book). Ah the wonders of Ruby!

Finally, there are a couple of examples in the later parts of the book which just didn’t fit into the ex##_*.rb naming scheme, but these should be pretty self explanatory.

If you have any questions or comments, just email me at or ping me on twitter @russolsen.


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