如何在初始化方法中幹掉我的ruby異常？

Question

我正在用一個Product類的Ruby編寫一個程序。每當使用錯誤類型的參數初始化Product時，我都會引發一些異常。有沒有一種方法可以幹掉我提出的例外情況（我甚至可以正確引用那些例外情況？）我很感激這種幫助。代碼如下：

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

慣用的方法是不行的類型檢查在所有的，而是強制的傳遞的對象（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 

然後你會得到適當的String/Float /等。傳遞對象的表示形式，以及如果他們不知道如何強制這些類型（因爲他們不響應該方法），那麼您將適當地得到一個NoMethodError。

至於在數量上的檢查，這看起來很像一個驗證，你可能要拔出到一個單獨的方法（特別是如果獲得是他們中的很多）：

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

你可以不喜歡以下，但我希望有寶石的是做到這一點，更多，更好地做到這一點：

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 

需要注意的是，在IRB運行時，Kernel#caller_locations帶來了很多的東西，你不」不需要，從命令行運行時不會得到。