Exceptions cheatsheet from Avdi Grimm talk

ruby_exceptions_cheatsheet.rb

# exceptions cheatsheet from Avdi Grimm talk

# talk: http://confreaks.net/videos/523-roa2011-exceptional-ruby


# retry

begin
rescue
  retry
end

# simple crash logger

at_exit do
  if $! # require 'English' #=> $ERROR_INFO
    # your_app_code
  end
end

# nested exceptions

class MyError < StandardError
  attr_reader :original
  def initialize(msg, original=$!)
   super msg
   @original = original
  end
end

# adding context

begin 
  f = File.open("/a_file")
rescue Exception => e
  raise e, "Useful message: #{e.message} - #{f.inspect}"
end
  
# implement #exception

class Net::HTTPResponse
  def exception(msg="HTTP Error")
    RuntimeError.new "#{message}: #{code}"
  end
end

response = Net::HTTP.get_response "http://makevoid.com/404"
raise response #=> HTTPError 404: NotFound


# system exit

begin
  # ...
  exit
rescue Exception => e
  puts "Rescued: #{e.inspect}, status: #{e.status}"
end
# prints: #<SystemExit: exit> ....
# and then continues!


# There are more that I didn't transcribed and there is an explanation of each one! so watch the video! http://confreaks.net/videos/523-roa2011-exceptional-ruby - @avdi

# more code snippets from his other presentation @railsconf

# http://avdi.org/talks/confident-code-railsconf-2011/


# pathname is more than a string

require 'pathname'
path = Pathname "/home/makevoid/.irb-history"
open path


# prefer Array() over .to_a

Array([1,2,3])    # => [1, 2, 3]
Array("foo")      # => ["foo"]
Array(nil)        # => []


# assertions

def assert(value, message="Assertion failed")
  raise Exception, message, caller unless value
end

options[:message] and
  assert(options[:message].to_s !~ /^\s*$/
  
# guard clause

def say(message, options={})
  return "" if message.nil?
  # ...
end

# kill nil: use fetch

{}.fetch(:required_opt)

opt = {}.fetch(:required_opt) do
  raise ArgumentError, "Missing option!"
end

options.fetch(:width) {40} # default value


# basic null object

class NullObject
  def method_missing(*args, &block)
    self
  end

  def nil?; true; end
end

def Maybe(value)
  value.nil? ? NullObject.new : value
end

# usage

def slug(text)
  Maybe(text).downcase.strip.tr_s('^a-z0-9', '-')
end

slug("Confident Code") # => "confident-code"
slug(nil)              # => #<NullObject:0xb780863c>


# popen - opens a pipe (not related but useful)

IO.popen("ls"){ |p| p.read.split }