00_README

Misplaced "ensures" in sample code from:
http://railsware.com/blog/2012/11/20/yield-gotcha-in-ruby-blocks/

Always be careful when adding "ensure" statements. Variables used within its
block may not have been assigned if an exception is raised within the "begin"
block. In fact, this mistake is often the result of not bothering with a "begin"
statement altogether

01_unsafe.rb

def ensured_with_file(name, &block)
  puts "Open file"
  f = File.open(name, "r")
  yield f
ensure
  #
  # /!\ f may be nil if File.open raises
  #
  puts "Close file"
  f.close
end

02_safe.rb

def ensured_with_file(name, &block)
  puts "Open file"
  f = File.open(name, "r")
  begin
    yield f
  ensure
    puts "Close file"
    f.close
  end
end