Ruby:NoMethodError:undefined方法`+'；零级：零级

有人知道为什么下面的代码返回错误吗

stock = {"M9788375085969"=>5, "M9788392289760"=>5, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2}
add = {"M9788375085969"=>1, "M9788392289760"=>2, "NEW9788392289753"=>1 }

add.each do |key, value|
  stock[key] += value
end

NoMethodError: undefined method `+' for nil:NilClass

虽然类似的方法也很管用：

key = "M9788375085969"
value = 1
stock[key] += value
=> 6

键

“NEW9788392289753”

不存在于散列

股票

中，但存在于

添加

散列中。见下文：

stock = {"M9788375085969"=>5, "M9788392289760"=>5, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2}
stock['NEW9788392289753'] # => nil
nil.respond_to?(:+) # => false # means NilClass don't has method called :+

因此，

nil.+（value）

抛出一个有效错误。按以下步骤进行：

stock = {"M9788375085969"=>5, "M9788392289760"=>5, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2}
add = {"M9788375085969"=>1, "M9788392289760"=>2, "NEW9788392289753"=>1 }

add.each do |key, value|
  p stock[key] += value if stock.has_key?(key) # it will take care of the error.
end

输出

6
7

根据OP的意见，我将采取以下措施：

add.each do |key, value|
  if stock.has_key?(key) 
     stock[key] += value 
  else
     stock[key] = value
  end
end

---

add

散列中有一个键在

stock

散列中丢失：“NEW9788392289753”

---

执行

stock[“NEW9788392289753”]

时，返回

nil

，因为键未映射。

因为

add

中的键

NEW9788392289753

未包含在

stock

中，处理不存在键的另一种方法是提供默认值零：

stock = {"M9788375085969"=>5, "M9788392289760"=>5, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2}
add = {"M9788375085969"=>1, "M9788392289760"=>2, "NEW9788392289753"=>1 }

stock.default = 0 

add.each do |key, value|
  stock[key] += value
end

p stock #=> {"M9788375085969"=>6, "M9788392289760"=>7, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2, "NEW9788392289753"=>1}

---

看起来很直截了当，不是吗？很漂亮。谢谢大家<代码>添加。每个do |键，值|开始库存[键]+=值拯救库存[键]=值结束。再次感谢。这也是一个好的、干净的、简单的解决方案。Ruby很漂亮，Ruby社区也是如此：）