I've finished reading "Metaprogramming Ruby"

I've finished reading Metaprogramming Ruby. This book is great book for:

• What metaprogramming is in Ruby
• Why do we do metaprogramming with Ruby
• How do we do metaprogramming by Ruby

But not only that, this is also great book for leaning what safe level is in Ruby. There are simple and lucid examples for leaning safe level. And, this book have taught me about nested irb.

irb(main):001:0> s = 'hello world'
=> "hello world"
irb(main):002:0> irb s
irb#1(hello world):001:0> upcase
=> "HELLO WORLD"
irb#1(hello world):002:0> exit
=> #<IRB::Irb: @context=#<IRB::Context:0x00000100849a30>, @signal_status=:IN_EVAL, @scanner=#<RubyLex:0x000001008454f8>>
irb(main):003:0> exit

I did not know at all until reading this book.