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)
