I really like your book, since a lot of design pattern courses mis out on mixing design patterns. I think the real power in patterns is if you make them work torgether.
In your book, you told us that "You can use Visitor to execute an operation over an entire Composite tree.". I tried this for mapping an object structure to another object structure. Something that's pretty common in the world of API's and database models.
I would really appreciate it if you would take a look at my following post question: https://codereview.stackexchange.com/q/240738/22130
And if not, I still enjoyed your book and learned a lot.
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