I assume you are responding to me. Yes, yes it is. From Wiki "Argumentum ad hominem, is an argument made personally against an opponent instead of against their argument." AlexeyBrin is implying that because greenyoda may not have written any programming books, that his argument is less valid. AlexeyBrin's argument is not refuting greenyoda's central point, that it's somewhat strange that the blog post author has written a programming book about Ruby, despite not being aware of what some argue are the language's commonly used features.

Clay wrote a book about RubyMotion (a Ruby compiler for iOS), not a book that teaches OOP. His knowledge about polymorphism is not so relevant for this book (I think he "knows" what polymorphism is but he was genuinely amazed by the way you can use it for this particular case).

> very valid

Validity is a binary state. Don't modify it with an adverb.

Just pointing that his little ad hominem attack has no place on HN.