Nil.to_s != "nil"

ruby-talk
1

Is it possible to change NilClass#to_s to return "nil"
rather than "" since "" != nil?

2

Eero Saynatkari wrote:

Is it possible to change NilClass#to_s to return "nil"
rather than "" since "" != nil?

-- test.rb BEGIN
p nil.to_s.nil?

class NilClass
  def to_s
    nil
  end
end

p nil
p nil.to_s.nil?
-- test.rb END

$ ruby test.rb
false
nil
true

···

--
Dmitri Priimak

3

Eero Saynatkari wrote:

Is it possible to change NilClass#to_s to return "nil"
rather than "" since "" != nil?

#!/usr/bin/ruby -w

class NilClass
  def to_s
    return "nil"
  end
end

p nil.to_s

"nil"

You may not want to do this. There might be a reason for the present
behavior. But it is very easy to do, as are all such changes in Ruby.

···

--
Paul Lutus
http://www.arachnoid.com

4

Eero Saynatkari wrote:

Is it possible to change NilClass#to_s to return "nil"
rather than "" since "" != nil?

1) #to_s should always return a string.
2) Any string representation will always be a truth value.

The same situation exists for false:
!!false.to_s #=> true

You are correct that "" != nil, but "nil" != nil also.
What are you really trying to achieve? And, did you know that
nil.inspect yields "nil"?

5

I should have been clearer. I was wondering if it could
be fixed in the language itself :slight_smile: Thank you though!

···

On 2006.10.27 13:56, Dmitri Priimak wrote:

Eero Saynatkari wrote:

>Is it possible to change NilClass#to_s to return "nil"
>rather than "" since "" != nil?
>
>
-- test.rb BEGIN
p nil.to_s.nil?

class NilClass
def to_s
   nil
end
end

p nil
p nil.to_s.nil?
-- test.rb END

$ ruby test.rb
false
nil
true

6

Paul Lutus wrote:

Eero Saynatkari wrote:

Is it possible to change NilClass#to_s to return "nil"
rather than "" since "" != nil?
    
#!/usr/bin/ruby -w

class NilClass
  def to_s
    return "nil"
  end
end

p nil.to_s

"nil"

You may not want to do this. There might be a reason for the present
behavior. But it is very easy to do, as are all such changes in Ruby.

I don't know what the real reason is, but it can be very useful when interpolating strings to have it be ""

-Justin

7

Eero Saynatkari wrote:
> Is it possible to change NilClass#to_s to return "nil"
> rather than "" since "" != nil?

1) #to_s should always return a string.

Right.

2) Any string representation will always be a truth value.

Yep.

The same situation exists for false:
!!false.to_s #=> true

true.to_s # => "true"
false.to_s # => "false"
nil.to_s # => ""

"" is not a valid representation of nil. "nil" is.

You are correct that "" != nil, but "nil" != nil also.
What are you really trying to achieve? And, did you know that
nil.inspect yields "nil"?

Yes. I want consistency.

···

On 2006.10.28 00:20, Phrogz wrote:

8

problem = nil

"but this is a #{ problem }"

-a

···

On Sat, 28 Oct 2006, Eero Saynatkari wrote:

You are correct that "" != nil, but "nil" != nil also.
What are you really trying to achieve? And, did you know that
nil.inspect yields "nil"?

Yes. I want consistency.

--
my religion is very simple. my religion is kindness. -- the dalai lama

9

Eero Saynatkari wrote:

···

On 2006.10.28 00:20, Phrogz wrote:
> You are correct that "" != nil, but "nil" != nil also.
> What are you really trying to achieve? And, did you know that
> nil.inspect yields "nil"?

Yes. I want consistency.

It is consistent. "to_s" returns a string representation of the
value(s) of the object you call it on.

The value of the object nil is _nothing_ and the empty string is a
sensible representation of that.

Vidar

10

Eero Saynatkari wrote:

You are correct that "" != nil, but "nil" != nil also.
What are you really trying to achieve? And, did you know that
nil.inspect yields "nil"?
    
Yes. I want consistency.
  

Ruby's behavior is consistent:

>> "a" + nil.to_s
# => "a"
>> 1 + nil.to_i
# => 1
>> 1.0 + nil.to_f
# => 1.0
>> [1] + nil.to_a
# => [1]

nil.to_X always returns the neutral element for #+. Of course Matz could have chosen some other kind of consistency instead of this one.

···

--
Florian Frank

11

problem = ''

"is it really a #{ problem }?"

Of course there's _tons_ of code out there that relies on nil.to_s being
the empty string. I don't expect it will change anytime soon.

···

On Sat, Oct 28, 2006 at 01:35:48AM +0900, ara.t.howard@noaa.gov wrote:

On Sat, 28 Oct 2006, Eero Saynatkari wrote:

>>You are correct that "" != nil, but "nil" != nil also.
>>What are you really trying to achieve? And, did you know that
>>nil.inspect yields "nil"?
>
>Yes. I want consistency.

problem = nil

"but this is a #{ problem }"

12

As well as sensible, it can be useful:

<code>
#! /usr/bin/env ruby -w

def bottles(n)
    "#{n} bottle#{'s' if n != 1} of beer on the wall"
end

bottles(99) # => "99 bottles of beer on the wall"
bottles(1) # => "1 bottle of beer on the wall"
</code>

Regards, Morton

···

On Oct 28, 2006, at 3:05 PM, Vidar Hokstad wrote:

Eero Saynatkari wrote:

On 2006.10.28 00:20, Phrogz wrote:

You are correct that "" != nil, but "nil" != nil also.
What are you really trying to achieve? And, did you know that
nil.inspect yields "nil"?

Yes. I want consistency.

It is consistent. "to_s" returns a string representation of the
value(s) of the object you call it on.

The value of the object nil is _nothing_ and the empty string is a
sensible representation of that.

13

Of course there's _tons_ of code out there that relies on nil.to_s being
the empty string. I don't expect it will change anytime soon.

Besides, we already have syntax that prevents this from being terribly
ugly anyway.

@foo = ""

=> ""

@foo.nil?

=> false

@foo.empty?

=> true

I like knowing the difference between an empty string and an undefined value.

···

On 10/28/06, Logan Capaldo <logancapaldo@gmail.com> wrote: