Advanced Rails - Building Industrial-Strength Web Apps in Record Time

Exception

66 | Chapter 2: ActiveSupport and RailTies

sum {|x| (x-m)**2} / length

end

def standard_deviation

variance ** 0.5

end

end

"%.2f" % [1,2,3,4,5].standard_deviation # => "1.41"

Exception core_ext/exception.rb

Four methods are added toException for more intuitive stack traces:

• clean_messageruns the exception message throughPathname.clean_within, which
  cleans any pathnames contained within the message (removes extra slashes and
  resolves. and.. paths).


• clean_backtraceruns the entire backtrace throughException::TraceSubstitutionsand
  Pathname.clean_within, to clean the pathnames.TraceSubstitutionsis used by Action-
  View’s templates to hide certain unsightly parts of the backtrace when template com-
  pilation fails.


• application_backtracereturns the set of frames belonging to the Rails application,
  excluding those that are part of the Rails framework.


• framework_backtracereturns the set of frames that are part of the Rails framework.
  Together withapplication_backtrace, this is used on the default Rails rescue pages in
  the development environment.

File core_ext/file.rb

File.atomic_writeatomically writes to a file; it creates a temporary file, yields it to a block
for writing, and then renames it to the destination. The advantage over a standard write is
that the destination file does not exist in a half-written state at any point.
File.atomic_write('important_file') do |important_file|
important_file.write data
end

Float core_ext/float.rb

Float#round rounds a floating-point number to the specified decimal place:

Math::PI # => 3.14159265358979

Math::PI.round # => 3

Math::PI.round(1) # => 3.1

Math::PI.round(2) # => 3.14

Math::PI.round(3) # => 3.142