Forum: Ruby differnce between .nil? , .empty?, .blank?

Hi
   Could you please tell me when to use .nil? , .empty?, .blank? .What
are the difference between them.. For example  I have
params[:company][:whichCompany]
And to check for it is null I first attempted all these and finally the
following worked
if !params[:company][:whichCompany].empty?

  So now really i am confused .Please tell me the differnce

Thanks in advance
Sijo

On Thu, Jul 24, 2008 at 9:00 AM, Sijo Kg <sijo@maxxion.com> wrote:

>   Could you please tell me when to use .nil? , .empty?, .blank? .What
> are the difference between them.. For example  I have
> params[:company][:whichCompany]
> And to check for it is null I first attempted all these and finally the
> following worked
> if !params[:company][:whichCompany].empty?
>
>  So now really i am confused .Please tell me the differnce

nil? tests whether the object is exactly nil, that is whether it is
the one and only want instance of NilClass.

empty? is a method some objects respond to. You need to check the
documentation for each case. For example, and empty array is one that
is not nil (it is an array right?) and has no elements. An empty
string is one that is not nil (it is a string right?) and has no
bytes, nothing.

The blank? method you ask for does not belong to Ruby, it is a Rails
extension: http://api.rubyonrails.com/classes/Object.html#M000011.

On Thursday 24 July 2008, Sijo Kg wrote:
> Thanks in advance
> Sijo

.nil? tests whether the receiver is the nil object, that is the only 
instance
of class NilClass, which is often used to indicate an invalid value. 
This
method is defined in class Object, and thus is availlable for every 
object.

The other two methods, instead, are defined only for specific classes, 
so the
answer depends. Usually, empty? is used to test whether an object is 
"empty",
for some class-depending meaning of empty. For example, String#empty? 
returns
true if the string contains no characters, Array#empty? and Hash#empty?
returns true if the array or hash has no entries. Other classes may 
define an
empty? method in other ways.  Note that, unlike nil?, empty? isn't 
defined for
all classes.

Regarding blank?, I never heard of it, so I can't help you. You should 
look at
the documentation of the class defining it.

Here are some examples about nil? and empty?

nil.nil?
=> true

false.nil?
=> false

1.nil?
=> false

0.nil?
=> false

"".nil?
=> false

[].nil?
=> false

"".empty?
=> true

"abc".empty?
=> false

[].empty?
=> true

[1, 2, 3].empty?
=> false

1.empty?
=> NoMethodError

The last example means that the empty? method is not defined for class 
Fixnum

I hope this helps

Stefano

Hi
  Thanks for all your reply.Now I understood
Sijo

Stefano Crocco wrote:

> Regarding blank?, I never heard of it

It's a Rails method on the Object class that 'combines' the test for 
nil?
and empty?.  Simplifies 'if thing.nil? || thing.empty?' to 'if
thing.blank?'.

Best regards,
Bill

Isn't .nil? and .empty? in a way testing for a very similar situation?

Some instance var:
  @colour = 'black'


Compared:
  @colour = ''
  @colour = nil


Which one to prefer of these?

Hi Marc,

Marc Heiler wrote:

> Isn't .nil? and .empty? in a way testing for a very similar
> situation?

Not in Ruby.  empty? is true for a String of length 0.  The value of the
String is not Nil.  It turns out that Nil is very important in 
evaluations
since it's one of the two items in Ruby that evaluates to false.

irb(main):001:0> str = String.new
=> ""
irb(main):002:0> str.length
=> 0
irb(main):003:0> if str then puts 'a zero-length string is still a 
string'
end
a zero-length string is still a string
=> nil
irb(main):004:0> str = nil
=> nil
irb(main):005:0> if str.nil? then puts 'assigning a nil value 
essentially
kills
the object' end
assigning a nil value essentially kills the object
=> nil.

HTH,
Bill

blank? is not only a combination.
blank? also test if there are printable characters in a string:

\n".empty?
=> false
"\n".blank?
=> true

Niklas Heinrich

On Thu, Jul 24, 2008 at 7:49 PM, Niklas Heinrich <niklas@pirabay.de> 
wrote:

> blank? is not only a combination.
> blank? also test if there are printable characters in a string:

More precisely any \S. Also false is blank? but the integer 0 is not.

Xavier Noria wrote:
> On Thu, Jul 24, 2008 at 9:00 AM, Sijo Kg <sijo@maxxion.com> wrote:
> 
>>   Could you please tell me when to use .nil? , .empty?, .blank? .What
>> are the difference between them.. For example  I have
>> params[:company][:whichCompany]
>> And to check for it is null I first attempted all these and finally the
>> following worked
>> if !params[:company][:whichCompany].empty?
>>
>>  So now really i am confused .Please tell me the differnce
> 
> nil? tests whether the object is exactly nil, that is whether it is
> the one and only want instance of NilClass.
> 
> empty? is a method some objects respond to. You need to check the
> documentation for each case. For example, and empty array is one that
> is not nil (it is an array right?) and has no elements. An empty
> string is one that is not nil (it is a string right?) and has no
> bytes, nothing.
> 
> The blank? method you ask for does not belong to Ruby, it is a Rails
> extension: http://api.rubyonrails.com/classes/Object.html#M000011.

This is answer was concise and helpful. Thanks!

I personally find this confusing:

>> a[:real]=false
>> a[:real]    => false
>> a[:real].blank?    => true    ??

if I populated a[:real] with false, why does '.blank?' return true? 
That's confusing. But hey, if you can't win them, join them. I love Ruby 
and Rails!

On Thu, Jul 15, 2010 at 7:45 AM, Michael Nissim <info@israelunique.com> 
wrote:

> I personally find this confusing:
>
>>> a[:real]=false
>>> a[:real]    => false
>>> a[:real].blank?    => true    ??
>
> if I populated a[:real] with false, why does '.blank?' return true?
> That's confusing. But hey, if you can't win them, join them. I love Ruby
> and Rails!

It should work

   $ script/console
   Loading development environment (Rails 2.3.2)
   >> a = {}
   => {}
   >> a[:real] = false
   => false
   >> a[:real].blank?
   => true

false is blank?, no matter where it is stored.