In Ruby Why Does Nil.Id Return 4

In Ruby why does nil.id return 4?

This is because nil is an object created when the language initializes, and that object's id happens to always be 4.

For more information about why the id happens to be 4, see this blog post.

Why does rails have 'which would mistakenly be 4' in the Called ID for nil error?

From ActiveSupport's NilClass extension:

#id exists in Ruby 1.8 (though it is deprecated). Since id is a fundamental method of Active Record models #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 config.whiny_nils determines whether this feature is enabled.
By default it is on in development and test modes, and it is off in
production mode.

Why am I getting a nil value from a Ruby object's member, when it is not nil?

I've solved the problem: chart.ScenarioID is the way I'd do it in C++ and it doesn't work here; it returns nil.

In Ruby, chart[:ScenarioID] works, and correctly returns 160.

Ruby syntax to avoid nil input being returned as zero

Because you're only calling super if the value is not nil, that means the value is NOT replaced when the value is nil. So if the value contained 0 then it'll still contain 0 afterwards.

If you want to be able to set the value to nil, you should do...

def mobile=(value)
  super(
    value.nil? ? nil : value.to_s.gsub(/\s+/, "").to_i
       )
end

Rails: id field is nil when calling Model.new

No, that's the correct behavior. When you create an object via new (as in your example), Rails doesn't persist it to the database (just in memory).

If you do Message.create, or Message.save like theIV said, then the id will be populated.

Creating instance of model in controller returns nil for id and timestamp Rails 6

In the default options of

belongs_to :user

require the user_id to be set in current versions of Rails. Because you do not assign a user to the new photo the photo cannot be saved.

To assign the current user to a new photo just change this line

@photo = Photo.new(photo_params)

in your create method in the controller to

@photo = current_user.photos.build(photo_params)

I advise reading the docs about the has_many association in the Rails Guides.

Object id of nil false true in rails 4?

Why is the object id of nil equal to 4? First, you need to know that false and true variables work exactly the same way as nil does. They are singleton instances of FalseClass and TrueClass, respectively. When the Ruby interpreter boots up, it initializes FalseClass, TrueClass and NilClass.

The result is:

false.object_id
=> 0

true.object_id
=> 2

nil.object_id
=> 4

What happened to 1 and 3? Well, the first bit is reserved for Fixnum values (numbers) only. Simple and consistent.

For getting the object ids of fixnum you may follow the formula:
object_id = (n*2)+1 [Where n is the fixnum]

---

Related Topics