Programming Ruby 2nd 读书笔记3

C08 Exceptions

1. 定义一个Exception

class MyException < StandardError
  def initialize(info)
    super(info)
  end
end    

 

2.  抛出并且捕获一个异常

require 'my_exception'

def raise_exception
  raise MyException.new("ERROR occurs!!!")
end

begin
  raise_exception()
rescue MyException => e
  print(e.backtrace.join("\n"))
end                           

 

3.  ensure和else

require 'my_exception'
def raise_exception_bycondition(num)
  if num != 5
    puts("num = #{num}")
  elsif num == 5
    puts("num = 5")
    raise MyException.new("Num == 5!!!")
  end
end
print("Input a number:")
end_num = Integer(gets)
begin
  for i in 1..end_num
    raise_exception_bycondition(i)
  end
  rescue MyException => e
    print(e.backtrace.join("\n"))
    puts()
  else
    puts("No MyException!")
  ensure
    puts("Alwasy ouput this sentense!")
end                                          

 

4. Retry

require 'my_exception'

def raise_exception_bycondition(raiseornot)
  if raiseornot
    raise MyException.new("Raise MyException!")
  else
    puts("Don't raise MyExcetpion!")
  end
end

$raiseornot = true
begin
  raise_exception_bycondition($raiseornot)
rescue MyException => e
  print(e.backtrace.join("\n"))
  puts()
  $raiseornot = false
  retry
end                 

 

5.  throw and catch 

def prompt_and_get(prompt)
  print prompt
  res = readline.chomp
  throw :quit_requested if res == "!"
  res
end
catch :quit_requested do
  name = prompt_and_get("Name: ")
  age = prompt_and_get("Age: ")
  sex = prompt_and_get("Sex: ")
  puts("name: #{name} -- Age: #{age} -- Sex: #{sex}")
end                                                                         

 

6.  caller在raise时的使用

require 'my_exception'

def raise_exception
  raise MyException, "ERROR occurs!!!", caller[1..-1]
end

def raise_exception2
  raise_exception
end

begin
  raise_exception2()
rescue MyException => e
  print(e.backtrace.join("\n"))
  puts()
end                                

 

结果显示是：

caller_sample.rb:12

 

C09 Modules

1.  Module

#module1.rb
module Module1
  Name = "Module1 Name"
  def Module1.info
    "Module1"
  end
end               

#module2.rb
module Module2
  Name = "Module2 Name"
  def Module2.info
    "Module2"
  end
end          

#module_sample.rb
require 'module1'
require 'module2'
puts(Module1.info)
puts(Module2.info)
puts(Module1::Name)
puts(Module2::Name)         

 

2. Mixin

#observable_mixin.rb
module Observable
  def observers
    @observer_list ||= []
  end
  def add_observer(obj)
    observers << obj
  end
  def notify_observers
    observers.each {|o| o.update }
  end
end    

#weather_info.rb
require 'observable_mixin'

class WeatherInfo
  include Observable
end

class WeatherShowForm1
  def update
    puts 'Weather update1'
  end
end

class WeatherShowForm2
  def update
    puts 'Weather update2'
  end
end

winfo = WeatherInfo.new()
winfo.add_observer(WeatherShowForm1.new)
winfo.add_observer(WeatherShowForm2.new)
winfo.notify_observers()

 

3. 名字查找顺序

Ruby looks first in the immediate class of an object, then in the mixins included into that class, and then in superclasses and their mixins. If a class has multiple modules mixed in, the last one included is searched first.