Errata for Programming Ruby 1.9 (3rd edition)

#49292: In "Ranges in Boolean Expressions," the account of the flip-flop mechanism does not tally with the samples (which do agree with the output from IRB). Also, the subheading reads "if expr1 .. expr1 / while expr1 .. expr1" rather than "if expr1 .. expr2 / while expr1 .. expr2." Though the following may be clumsily written compared to the rest of the book, it does at least describe what actually happens:

#Ranges in Boolean Expressions

if expr1 .. expr2
while expr1 .. expr2

A range used in a boolean expression acts as a flip-flop. It has two states, set and unset, and is initially unset.

In the three-dot form, when the condition is executed and the flip-flop is unset, Ruby checks the truth of expr1. If true, the flip-flop becomes set and the condition returns true.

When the condition is executed with the flip-flop set, Ruby checks the truth of expr2. If false, the expression returns true and the state of the flip-flop remains set. If, on the other hand, expr2 returns true, the condition still returns true but the flip-flop is unset.

The two-dot form works the same way, except that the state of the flip-flop does not change from unset to set if expr1 is true but expr2 is also true.--Benjamin Rowlinson

#48531: (This _might_ be more of suggestion for clarifying the content.)

In the description of the Binding class, the text says:

"The variables, methods, value of self, and possibly an iterator block accessible in this context are all retained."

That sounds like you can access the methods as they were where/when the binding is created, which is not necessarily the case. If the example Demo class were originally defined with a `:hullo_world` method that is modified by re-opening the class definition _after_ setting `b1 = k1.get_binding` (`b1 = ...` is from your example), running `eval 'hullo_world', b1` would use the _new_ definition of :hullo_world.

Or if `:hullo_world` were only added to the class after the binding is created, running `eval 'hullo_world', b1` would still use the new definition of `:hullo_world`.

Does that make sense? ...It's really the scope where the binding is made that is retained and not necessarily all the items available at that point.

Unless I'm misunderstanding everything! Send me a quick email if that's the case so I know?

Thanks!

Scott--Scott Steele

#48020: The description of the sleep method says "An argument
of zero causes sleep to sleep forever". And the signature shows 0 as the default value of the argument to sleep. In fact, an argument of 0 causes sleep to sleep for 0 seconds, i.e. not at all. Fortunately the default value of the argument to sleep is nil, which does cause sleep to sleep forever!--Ray Bovet

#48456: The documentation for String#ord states in part "Note that it isn’t quite the inverse of Integer#chr, because the latter does not deal with encodings." However, Integer#chr does take an Encoding argument. So, for example, assuming UTF-8 encoding, "ありがと".ord.chr(Encoding::UTF_8) should == "あ". The argument to chr would be unnecessary if the -U command line option were given.--Brian Ford