创建一个引发类特定错误的模块 [英] Creating a module for raising class-specific errors

问题描述

在我的rails项目中，我经常在类和模型中使用这种行为:

In my rails projects, I often use this sort of behavior in my classes and models:

class Whatever

  class WhateverError < StandardError; end

  def initialize(params={})
    raise WhateverError.new("Bad params: #{params}") if condition
    # actual class code to follow
  end
end

麻烦的是，这既重复又很冗长.如果可以在需要引发特定于类的错误时执行此操作，我将非常喜欢:

The trouble is, this is both hugely repetitive and fairly verbose. I'd love it if I could just do this whenever I need to raise a class-specific error:

class ErrorRaiser
  include ClassErrors
  def initialize(params={})
    error("Bad params: #{params}") if condition
    error if other_condition # has default message
    # actual class code to follow
  end

  def self.class_method
    error if third_condition # class method, behaves identically
  end
end

我在创建这样的模块时遇到了很大的麻烦.我早期的尝试很可悲，如下所示，但是我对模块范围内的可用内容，如何动态创建类(在方法内?)或是否具有简单的.

I'm having major trouble creating such a module. My sad early attempts have tended to look something like the below, but I'm pretty confused about what's available within the scope of the module, how to dynamically create classes (within methods?) or whether I have straightforward access to the "calling" class at all.

我的基本要求是，error既要是类方法又要是实例方法，必须被命名空间"给调用它的类，并且要有默认消息.有什么想法/帮助吗?这有可能吗?

My basic requirements are that error be both a class method and an instance method, that it be "namespaced" to the class calling it, and that it have a default message. Any thoughts/help? Is this even possible?

module ClassErrorable 

  # This and the "extend" bit (theoretically) allow error to be a class method as well
  module ClassMethods
    def self.error(string=nil)
      ClassErrorable.new(string).error
    end
  end

  def self.included(base)
    set_error_class(base)
    base.extend ClassMethods
  end

  def self.set_error_class(base)
    # I'm shaky on the scoping. Do I refer to this with @ in a class method
    # but @@ in an instance method? Should I define it here with @ then?
    @@error_class = "##{base.class}Error".constantize
  end

  def self.actual_error
    # This obviously doesn't work, and in fact,
    # it raises a syntax error. How can I make my 
    # constant a class inheriting from StandardError?
    @@actual_error = @@error_class < StandardError; end 
  end

  def initialize(string)
    @string = string || "There's been an error!"
  end

  def error(string=nil)
    raise @@actual_error.new(string)
  end

end

推荐答案

这样的事情(用纯Ruby编写；可以重构为使用一些特定于Rails的功能，例如.constantize):

How about something like this (written in pure Ruby; it could be refactored to use some Rails-specific features like .constantize):

module ClassErrorable 
  module ClassMethods
    def error(message = nil)
      klass = Object::const_get(exception_class_name)
      raise klass.new(message || "There's been an error!")
    end

    def exception_class_name
      name + 'Error'  
    end
  end

  def self.included(base)
    base.extend ClassMethods
    Object::const_set(base.exception_class_name, Class.new(Exception))
  end

  def error(message = nil)
    self.class.error(message)
  end
end

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