Ruby中的异常处理代码编写示例

技术  /  管理员 发布于 6年前   306

单个异常使用 fail 关键字仅仅当捕获一个异常并且反复抛出这个异常(因为这里你不是失败，而是准确的并且故意抛出一个异常)。

  begin   fail 'Oops'  rescue => error   raise if error.message != 'Oops'  end

    不要为 fail/raise 指定准确的 RuntimeError。

   

 # bad  fail RuntimeError, 'message'  # good - signals a RuntimeError by default  fail 'message'

    宁愿提供一个异常类和一条消息作为 fail/raise 的两个参数，而不是一个异常实例。

   

 # bad  fail SomeException.new('message')  # Note that there is no way to do `fail SomeException.new('message'), backtrace`.  # good  fail SomeException, 'message'  # Consistent with `fail SomeException, 'message', backtrace`.

    不要在 ensure 块中返回。如果你明确的从 ensure 块中的某个方法中返回，返回将会优于任何抛出的异常，并且尽管没有异常抛出也会返回。实际上异常将会静静的溜走。

  

 def foo   begin    fail   ensure    return 'very bad idea'   end  end

    Use implicit begin blocks when possible.如果可能使用隐式 begin 代码块。

   

 # bad  def foo   begin    # main logic goes here   rescue    # failure handling goes here   end  end  # good  def foo   # main logic goes here  rescue   # failure handling goes here  end

    通过 contingency methods 偶然性方法。 (一个由 Avdi Grimm 创造的词) 来减少 begin 区块的使用。

 

  # bad  begin   something_that_might_fail  rescue IOError   # handle IOError  end  begin   something_else_that_might_fail  rescue IOError   # handle IOError  end  # good  def with_io_error_handling    yield  rescue IOError   # handle IOError  end  with_io_error_handling { something_that_might_fail }  with_io_error_handling { something_else_that_might_fail }

    不要抑制异常输出。

 

  # bad  begin   # an exception occurs here  rescue SomeError   # the rescue clause does absolutely nothing  end  # bad  do_something rescue nil

    避免使用 rescue 的修饰符形式。

   

 # bad - this catches exceptions of StandardError class and its descendant classes  read_file rescue handle_error($!)  # good - this catches only the exceptions of Errno::ENOENT class and its descendant classes  def foo   read_file  rescue Errno::ENOENT => ex   handle_error(ex)  end

    不要用异常来控制流。

   

 # bad  begin   n / d  rescue ZeroDivisionError   puts "Cannot divide by 0!"  end  # good  if d.zero?   puts "Cannot divide by 0!"  else   n / d  end

    应该总是避免拦截(最顶级的) Exception 异常类。这里(ruby自身)将会捕获信号并且调用 exit，需要你使用 kill -9 杀掉进程。

 

  # bad  begin   # calls to exit and kill signals will be caught (except kill -9)   exit  rescue Exception   puts "you didn't really want to exit, right?"   # exception handling  end  # good  begin   # a blind rescue rescues from StandardError, not Exception as many   # programmers assume.  rescue => e   # exception handling  end  # also good  begin   # an exception occurs here  rescue StandardError => e   # exception handling  end

    将更具体的异常放在救援（rescue）链的上方，否则他们将不会被救援。

  # bad  begin   # some code  rescue Exception => e   # some handling  rescue StandardError => e   # some handling  end  # good  begin   # some code  rescue StandardError => e   # some handling  rescue Exception => e   # some handling  end

    在 ensure 区块中释放你程式获得的外部资源。

  

 f = File.open('testfile')  begin   # .. process  rescue   # .. handle error  ensure   f.close unless f.nil?  end

    除非必要, 尽可能使用 Ruby 标准库中异常类，而不是引入一个新的异常类。(而不是派生自己的异常类)