Question

我正在使用Product类在Ruby中编写程序。每当使用错误类型的参数初始化Product时，我都会引发一些异常。有没有办法可以减少我提出的异常（我甚至指的是正确的？）我很感激你的帮助。代码如下：

class Product
  attr_accessor :quantity, :type, :price, :imported

  def initialize(quantity, type, price, imported)
    raise ArgumentError.new("Type must be a string") if type.class != String
    raise ArgumentError.new("Quantity must be greater than zero") if quantity <= 0
    raise ArgumentError.new("Price must be a float") if price.class != Float

    @quantity = quantity
    @type     = type
    @price    = price.round(2)
    @imported = imported
  end
end

Answer 1

惯用的方法是根本不进行类型检查，而是强制传递的对象（使用to_s，to_f等）：

class Product
  attr_accessor :quantity, :type, :price, :imported

  def initialize(quantity, type, price, imported)
    raise ArgumentError.new("Quantity must be greater than zero") unless quantity > 0

    @quantity = quantity
    @type     = type.to_s
    @price    = price.to_f.round(2)
    @imported = imported
  end
end

然后您将获得适当的String / Float / etc。传递的对象的表示，如果他们不知道如何被强制转换为那些类型（因为他们没有响应那个方法），那么你将适当地得到一个NoMethodError。

对于数量检查，这看起来很像验证，你可能想要提取到一个单独的方法（特别是如果它们有很多）：

class Product
  attr_accessor :quantity, :type, :price, :imported

  def initialize(quantity, type, price, imported)
    @quantity = quantity
    @type     = type.to_s
    @price    = price.to_f.round(2)
    @imported = imported

    validate!
  end

  private

  def validate!
    raise ArgumentError.new("Quantity must be greater than zero") unless @quantity > 0
  end
end

Answer 2

class Product
  attr_accessor :quantity, :type, :price, :imported

  def initialize(quantity, type, price, imported)
    raise ArgumentError.new "Type must be a string" unless type.is_a?(String)
    raise ArgumentError.new "Quantity must be greater than zero" if quantity.zero?
    raise ArgumentError.new "Price must be a float" unless price.is_a?(Float)

    @quantity, @type, @price, @imported = quantity, type, price.round(2), imported
  end
end

Answer 3

你可以做类似下面的事情，虽然我希望有宝石可以做到这一点以及更多，并做得更好：

module ArgCheck
  def type_check(label, arg, klass)
    raise_arg_err label + \
      " (= #{arg}) is a #{arg.class} object, but should be be a #{klass} object" unless arg.is_a? klass
  end

  def range_check(label, val, min, max)
    raise_arg_err label + " (= #{val}) must be between #{min} and #{max}" unless val >= min && val <= max
  end

  def min_check(label, val, min)
  puts "val = #{val}, min = #{min}"
    raise_arg_err label + " (= #{val})  must be >= #{min}" unless val >= min
  end

  def max_check(val, min)
    raise_arg_err label + " (= #{val})  must be <= #{max}" unless val <= max
  end    

  # Possibly other checks here  

  private

  def raise_arg_err(msg)
    raise ArgumentError, msg + "\n  backtrace: #{caller_locations}"
  end   
end

class Product
  include ArgCheck 
  attr_accessor :quantity, :type, :price, :imported

  def initialize(quantity, type, price)
    # Check arguments  
    min_check   'quantity', quantity, 0
    type_check  'type',     type,     String
    type_check  'price',    price,    Float

    @quantity = quantity
    @type     = type
    @price    = price.round(2)
  end
end

product = Product.new(-1, :cat, 3)
#  => arg_check.rb:23:in `raise_arg_err': quantity (= -1)  must be >= 0 (ArgumentError)
#    backtrace: ["arg_check.rb:11:in `min_check'", "arg_check.rb:33:in `initialize'", \
#      "arg_check.rb:43:in `new'", "arg_check.rb:43:in `<main>'"]

product = Product.new(1, :cat, 3)
#  => arg_check.rb:26:in `raise_arg_err': type (= cat) is a Symbol object, \
#       but should be be a String object (ArgumentError)
#       backtrace: ["arg_check.rb:3:in `type_check'", "arg_check.rb:34:in `initialize'", \
#         "arg_check.rb:48:in `new'", "arg_check.rb:48:in `<main>'"]

product = Product.new(1, "cat", 3)
#  => arg_check.rb:23:in `raise_arg_err': price (= 3) must be a Float object (ArgumentError)
#       backtrace: ["arg_check.rb:3:in `type_check'", "arg_check.rb:35:in `initialize'", \
#       "arg_check.rb:53:in `new'", "arg_check.rb:53:in `<main>'"]

product = Product.new(1, "cat", 3.00) # No exception raised

请注意，在irb中运行时，Kernel#caller_locations会带来许多你不想要的东西，从命令行运行时你不会得到它。

如何在初始化方法中干掉我的ruby异常？

3 个答案: