Question

我似乎无法找到有关自定义异常类的更多信息。

我所知道的

您可以声明自定义错误类，并让它继承自StandardError，因此它可以是rescue d：

class MyCustomError < StandardError
end

这允许你使用：

来提高它

raise MyCustomError, "A message"

以后，在救援时获取该消息

rescue MyCustomError => e
  puts e.message # => "A message"

我不知道

我想为我的异常提供一些自定义字段，但我想从父类继承message属性。我发现读on this topic @message不是异常类的实例变量，所以我担心我的继承不起作用。

有人可以给我更多细节吗？如何实现具有object属性的自定义错误类？以下是正确的：

class MyCustomError < StandardError
  attr_reader :object
  def initialize(message, object)
    super(message)
    @object = object
  end
end

然后：

raise MyCustomError.new(anObject), "A message"

得到：

rescue MyCustomError => e
  puts e.message # => "A message"
  puts e.object # => anObject

它会起作用，如果确实如此，这是正确的做事方式吗？

Answer 1

raise已设置消息，因此您无需将其传递给构造函数：

class MyCustomError < StandardError
  attr_reader :object

  def initialize(object)
    @object = object
  end
end

begin
  raise MyCustomError.new("an object"), "a message"
rescue MyCustomError => e
  puts e.message # => "a message"
  puts e.object # => "an object"
end

我已将rescue Exception替换为rescue MyCustomError，请参阅Why is it a bad style to `rescue Exception => e` in Ruby?。

Answer 2

鉴于Exception的ruby核心文档，其中所有其他错误都继承了该文档，请说明#message

返回调用exception.to_s的结果。通常这会返回异常的消息或名称。通过提供to_str方法，异议同意在预期字符串的情况下使用。

http://ruby-doc.org/core-1.9.3/Exception.html#method-i-message

我会选择重新定义to_s / to_str或初始化程序。以下是一个示例，我们希望以外部服务无法执行某些操作的方式以人类可读的方式了解这些内容。

注意：下面的第二个策略使用rails pretty字符串方法，例如demodualize，这可能有点复杂，因此在异常中可能不明智。如果需要，您还可以为方法签名添加更多参数。

覆盖#to_s策略 而不是#to_str，它的工作方式不同

module ExternalService

  class FailedCRUDError < ::StandardError
    def to_s
      'failed to crud with external service'
    end
  end

  class FailedToCreateError < FailedCRUDError; end
  class FailedToReadError < FailedCRUDError; end
  class FailedToUpdateError < FailedCRUDError; end
  class FailedToDeleteError < FailedCRUDError; end
end

控制台输出

begin; raise ExternalService::FailedToCreateError; rescue => e; e.message; end
# => "failed to crud with external service"

begin; raise ExternalService::FailedToCreateError, 'custom message'; rescue => e; e.message; end
# => "failed to crud with external service"

begin; raise ExternalService::FailedToCreateError.new('custom message'); rescue => e; e.message; end
# => "failed to crud with external service"

raise ExternalService::FailedToCreateError
# ExternalService::FailedToCreateError: failed to crud with external service

覆盖#initialize策略

这是与我在rails中使用的实现最接近的策略。如上所述，它使用demodualize，underscore和humanize ActiveSupport方法。但这可以很容易地删除，就像之前的策略一样。

module ExternalService
  class FailedCRUDError < ::StandardError
    def initialize(service_model=nil)
      super("#{self.class.name.demodulize.underscore.humanize} using #{service_model.class}")
    end
  end

  class FailedToCreateError < FailedCRUDError; end
  class FailedToReadError < FailedCRUDError; end
  class FailedToUpdateError < FailedCRUDError; end
  class FailedToDeleteError < FailedCRUDError; end
end

控制台输出

begin; raise ExternalService::FailedToCreateError; rescue => e; e.message; end
# => "Failed to create error using NilClass"

begin; raise ExternalService::FailedToCreateError, Object.new; rescue => e; e.message; end
# => "Failed to create error using Object"

begin; raise ExternalService::FailedToCreateError.new(Object.new); rescue => e; e.message; end
# => "Failed to create error using Object"

raise ExternalService::FailedCRUDError
# ExternalService::FailedCRUDError: Failed crud error using NilClass

raise ExternalService::FailedCRUDError.new(Object.new)
# RuntimeError: ExternalService::FailedCRUDError using Object

演示工具

这是一个展示上述实施的救援和消息传递的演示。引发异常的类是Cloudinary的伪API。只需将上述策略之一转储到rails控制台，然后再进行此操作。

require 'rails' # only needed for second strategy 

module ExternalService
  class FailedCRUDError < ::StandardError
    def initialize(service_model=nil)
      @service_model = service_model
      super("#{self.class.name.demodulize.underscore.humanize} using #{@service_model.class}")
    end
  end

  class FailedToCreateError < FailedCRUDError; end
  class FailedToReadError < FailedCRUDError; end
  class FailedToUpdateError < FailedCRUDError; end
  class FailedToDeleteError < FailedCRUDError; end
end

# Stub service representing 3rd party cloud storage
class Cloudinary

  def initialize(*error_args)
    @error_args = error_args.flatten
  end

  def create_read_update_or_delete
    begin
      try_and_fail
    rescue ExternalService::FailedCRUDError => e
      e.message
    end
  end

  private def try_and_fail
    raise *@error_args
  end
end

errors_map = [
  # Without an arg
  ExternalService::FailedCRUDError,
  ExternalService::FailedToCreateError,
  ExternalService::FailedToReadError,
  ExternalService::FailedToUpdateError,
  ExternalService::FailedToDeleteError,
  # Instantiated without an arg
  ExternalService::FailedCRUDError.new,
  ExternalService::FailedToCreateError.new,
  ExternalService::FailedToReadError.new,
  ExternalService::FailedToUpdateError.new,
  ExternalService::FailedToDeleteError.new,
  # With an arg
  [ExternalService::FailedCRUDError, Object.new],
  [ExternalService::FailedToCreateError, Object.new],
  [ExternalService::FailedToReadError, Object.new],
  [ExternalService::FailedToUpdateError, Object.new],
  [ExternalService::FailedToDeleteError, Object.new],
  # Instantiated with an arg
  ExternalService::FailedCRUDError.new(Object.new),
  ExternalService::FailedToCreateError.new(Object.new),
  ExternalService::FailedToReadError.new(Object.new),
  ExternalService::FailedToUpdateError.new(Object.new),
  ExternalService::FailedToDeleteError.new(Object.new),
].inject({}) do |errors, args|
  begin 
    errors.merge!( args => Cloudinary.new(args).create_read_update_or_delete)
  rescue => e
    binding.pry
  end
end

if defined?(pp) || require('pp')
  pp errors_map
else
  errors_map.each{ |set| puts set.inspect }
end

Answer 3

你的想法是正确的，但你所说的方式是错误的。它应该是

raise MyCustomError.new(an_object, "A message")

Answer 4

我想做类似的事情。我想将一个对象传递给#new，并根据传递对象的某些处理设置消息。以下作品。

class FooError < StandardError
  attr_accessor :message # this is critical!
  def initialize(stuff)
    @message = stuff.reverse
  end
end

begin
  raise FooError.new("!dlroW olleH")
rescue FooError => e
  puts e.message #=> Hello World!
end

请注意，如果您未声明attr_accessor :message，那么它将无效。解决OP的问题，您还可以将消息作为附加参数传递并存储您喜欢的任何内容。关键部分似乎是重写#message。

Ruby自定义错误类：message属性的继承

4 个答案: