Ruby Hacking Guide
by Minero Aoki
The RHG is a book that explains how the ruby interpreter (the official C implementation of the Ruby language) works internally. To fully understand it, you need a good knowledge of C and Ruby. This book is going to investigate ruby as a whole.
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by Huw Collingbourne - No Starch Press
A comprehensive tutorial to the Ruby language. Each chapter is accompanied by ready-to-run source code for all the examples. There is also an Introduction which explains how to use the source code in Ruby In Steel or any other IDE of your choice.
by Bruno R. Preiss
The primary goal of this book is to promote object-oriented design using Ruby and to illustrate the use of the emerging object-oriented design patterns. The book shows how these patterns are used to create good software designs.
by Matt Aimonetti - O'Reilly Media
MacRuby is Apple's implementation of the Ruby programming language which uses Objective-C runtime. This book is an introduction to MacRuby. Topics covered: Introduction, The Cocoa Environment, Foundation, Application Kit, Core Data, Xcode.
by Gregory T. Brown - O'Reilly Media
Ruby Best Practices aims to help Ruby developers from a wide range of skill levels improve their fundamental understanding of the language via exposure to the common practices and idioms that many seasoned Rubyists take for granted.