This document contains examples of error handling in Ruby using exceptions, rescue blocks, and custom error classes. It demonstrates raising different types of errors, accessing error details, and ensuring code is run after exceptions.

2. Array.hello
#NoMethodError: undefined method `hello' for Array:Class
#from (irb):3
#from /home/vladimir/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'
hello
#NameError: undefined local variable or method `hello' for main:Object
#from (irb):4
#from /home/vladimir/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'

4. def my_method()
raise "SomeError message ..." # raise "m" == raise RuntimeError.new("m")
end
my_method
#exceptions.rb:2:in `my_method': SomeError message ... (RuntimeError)
#from exceptions.rb:5:in `<main>'

5. class Book
attr_accessor :author, :page_count, :title
def initialize(args = {})
@author = args[:author]
self.page_count = args[:page_count]
@title = args[:title]
end
def page_count=(value)
min, max = 1, 1000
if value < min || value > max
raise RangeError, "Value of [#{value}] outside bounds of [#{min}] to
[#{max}]."
else
@page_count = value
end
end
end

6. begin
100 / 0
rescue
puts "F! Divider is zero!"
end
#=> F! Divider is zero!

7. begin
some_undefined_method_call
rescue NameError
puts "F! Undefined method!"
end
#=>F! Undefined method!
def hello(msg = "")
raise "Empty message!" if msg == ""
puts(msg)
rescue
puts "Some Error!"
end
hello("Rubydev.ru") #Rubydev.ru
hello #Some Error!

8. begin
some_undefined_method_call
rescue NameError
p "F! Undefined method!"
ensure
p "RubyDev.ru"
end
#=>"F! Undefined method!"
#=>"RubyDev.ru"

9. begin
3 / 0
rescue ZeroDivisionError => e
puts "#{e.class}: #{e.message}"
end
begin
"my string".odd?
rescue NoMethodError => e
puts "#{e.class}: #{e.message}"
end

10. class MyError < StandardError
attr_reader :thing
def initialize(msg="My default message", thing="apple")
@thing = thing
super(msg)
end
end
begin
raise MyError.new("my message", "my thing")
rescue => e
puts e.thing # "my thing"
end