When comparing The Bastards Book of Ruby vs Ruby Koans, the Slant community recommends Ruby Koans for most people. In the question“What are the best resources to learn Ruby?” Ruby Koans is ranked 8th while The Bastards Book of Ruby is ranked 10th. The most important reason people chose Ruby Koans is:
Available online for free.
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Pros
Pro Free
Available for free online.
Pro Free
Available online for free.
Cons
Con Currently little activity from the writers
This series, which is great, has not seen many updates from the developers who are writing the project. It appears that this is because they have had to focus their time in other more pressing development projects. But currently, it doesn't appear that this resources is entirely active. However, it's great in content and quality, so I would suggest checking for future updates.