Errata for Programming Ruby 1.9

#39554: The paragraph under 'Interactive Configuration' says: "For example to change your prompt back to DEFAULT you could use the following:" but then the code is 'conf.prompt_mode = :SIMPLE'.--Octav Popescu

#39185: I can not reproduce the behavior of class variable as described on pages 337 and 338 of Programming Ruby 1.9.

Here is a file with Ruby code I typed in from the text:

##### begin classvars.rb
class Holder
@@var = 99
def Holder.var=(val)
@@var = val
end
def var
@@var
end
end

@@var = "top level variable"

a = Holder.new
puts "a.var: #{a.var}"
Holder.var = 123
puts "a.var: #{a.var}"

def a.get_var
@@var
end

puts "a.get_var: #{a.get_var}"
puts "@@var: #{@@var}"
##### end classvars.rb

(Essentially, this is the code from the text using puts to produce output. Also, at the end, I show the value of the top level variable @@var.)

Here is the Ruby version and the output I see:

$ ruby -v
ruby 1.9.1p0 (2009-01-30 revision 21907) [i686-linux]
$ ruby classvars.rb
a.var: top level variable
a.var: 123
a.get_var: 123
@@var: 123--Kenneth Ballou (ballou@crab.mv.com)

#39186: With respect to erratum #39185, I tried the same code on an older Ruby build:

$ ruby -v
1.9.0 (2006-06-08) [x86_64-linux]

With this version, the output agrees with the text:

$ ruby1.9 classvars.rb
a.var: 99
a.var: 123
a.get_var: top level variable
@@var: top level variable

Perhaps this is a Ruby bug in 1.9.1p0 instead of a book erratum?--Kenneth Ballou

#39435: The second paragraph for section "break, redo, next, and retry" says: "retry restarts the loop, reevaluating the condition." However on page 147 there's a footnote saying "Prior versions of Ruby also supported the retry keyword as a looping mechanism. This has been removed in Ruby 1.9."--Octav Popescu

#39292: Description of $stdout states: "Assignment to $stdout is not permitted: use $stdout.reopen instead."

I believe this is not exact. STDOUT can't be reassigned (obviously since it is a constant), but $stdout is a variable and has STDOUT as default value, but can be reassigned. See The Ruby Programming Language, for intance to section 9.7.1.4, or search ruby's source code for "$stdout = "--Marc-Andre Lafortune

#39444: First paragraph for 'Calling a Proc' says: "You can call a proc by invoking its methods call, yield, or []. The three forms are identical." No examples is given for the third form. I doubt it's really identical to the others. Usually when calling a [] method you need to put something between the brackets.--Octav Popescu

#39445: Second paragraph for 'Calling a Proc' says: "You can also invoke a proc using the syntax name.(args...). This is mapped internally into a.call(...)." Who's 'a' and where do 'name' and 'args' go? Maybe it wants to say "name.call(args...)"?--Octav Popescu

#39188: Hash.[] has two other forms. The second and third form take a single argument which is either an array of key-value pairs or an object convertible to a hash.

See redmine #1385, confirmed ruby-core #23433--Marc-Andre Lafortune

#39050: Oups, sorry, I meant to say Numeric#step returns an enumerator if no block is given (in Ruby 1.9), so the interface should change, and a "1.9" symbol should be added.--Marc-Andre Lafortune

#39135: The 'members' instance method of Struct returns an array of symbols rather than strings, and this is a change in 1.9.

members joe.members →array
Returns an array of strings (s/b symbols) representing the names of the instance variables.
Customer = Struct.new(:name, :address, :zip)
joe = Customer.new("Joe Smith", "123 Maple, Anytown NC", 12345)
joe.members # => [:name, :address, :zip]--Garold L Johnson