名爲id爲Rails 3的

Question

零在發展模式：

nil.id 
=> "Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id" 

在生產模式：

nil.id 
=> 4 

爲什麼？

Answer 1

查找行，說你的環境CONFIGS如下：

# Log error messages when you accidentally call methods on nil. 
config.whiny_nils = true # or false in production.rb 

這是爲了防止你打電話，而在發展模式上nil方法。我想他們出於性能原因在生產中禁用了它。

和nil是ruby中的單例對象，這就是爲什麼它的id將是4的原因。

Answer 2

你development.rb環境現狀有如下一行：

config.whiny_nils = true 

當您嘗試調用一個方法上nil這將記錄一個錯誤。 nil的ID是4，因爲it is an object which happens to have an id of 4

Answer 3

只有在開發模式（查看您的配置文件）中才報告Whiny nils。

「嘀咕尼爾斯」是把警告轉化每當方法被調用，在零值，以（希望）有用 關於哪些類型的對象，你可能一直在試圖 日誌 Rails的項使用。

Answer 4

方法NilClass#id的代碼具有很好的解釋：

# NilClass#id exists in Ruby 1.8 (though it is deprecated). Since +id+ is a fundamental 
# method of Active Record models NilClass#id is redefined as well to raise a RuntimeError 
# and warn the user. She probably wanted a model database identifier and the 4 
# returned by the original method could result in obscure bugs. 
# 
# The flag <tt>config.whiny_nils</tt> determines whether this feature is enabled. 
# By default it is on in development and test modes, and it is off in production 
# mode. 

https://github.com/rails/rails/blob/0c76eb1106dc82bb0e3cc50498383d6f992da4fb/activesupport/lib/active_support/whiny_nil.rb#L19