Concatenating strings with nil values

ruby-talk
1

Hi *,

I like to concatenate a string out of some variables, some of which
are nil. Instead of getting always a "can't convert nil into String
(TypeError)" message, I would like to have "nil" appended to my
string, as in Java null objects are printed as null in Strings.
Something like this:

words = Hash.new
words[0]="one"
allWords = "all words:"
allWords << words[0]
allWords << words[1]
# --> can't convert nil into String (TypeError)

Is this possible? Or how can I handle nil objects for this case?

Thanks.

2

Is this what you are looking for?

http://www.rubycentral.com/book/ref_c_hash.html#Hash.new

Harry

···

On 2/23/07, tchick <monsorno-nospam@gmx.de> wrote:

Hi *,

I like to concatenate a string out of some variables, some of which
are nil. Instead of getting always a "can't convert nil into String
(TypeError)" message, I would like to have "nil" appended to my
string, as in Java null objects are printed as null in Strings.
Something like this:

words = Hash.new
words[0]="one"
allWords = "all words:"
allWords << words[0]
allWords << words[1]
# --> can't convert nil into String (TypeError)

Is this possible? Or how can I handle nil objects for this case?

Thanks.

--

3

Hi.
There are some ways to do it. The simplest I can suggest is:

allWords << (w[1] || "nil")

with the disadvantage you'd have to state it everywhere you expect a
nil value.

Another way is

class String
  alias old_concat <<
  def <<(something)
    something = "nil" if something.nil?
    old_concat(something)
  end
end

in which case is not recommended to mess up with core classes.

···

On Feb 23, 7:55 am, "tchick" <monsorno-nos...@gmx.de> wrote:

Hi *,

I like to concatenate a string out of some variables, some of which
are nil. Instead of getting always a "can't convert nil into String
(TypeError)" message, I would like to have "nil" appended to my
string, as in Java null objects are printed as null in Strings.
Something like this:

Is this possible? Or how can I handle nil objects for this case?

Thanks.

4

If you're adventerous (ie. your code is essentially standalone and in
no danger of effecting others):

  class NilClass
    def to_str
      ""
    end
  end

T.

···

On Feb 23, 9:00 am, "tchick" <monsorno-nos...@gmx.de> wrote:

Hi *,

I like to concatenate a string out of some variables, some of which
are nil. Instead of getting always a "can't convert nil into String
(TypeError)" message, I would like to have "nil" appended to my
string, as in Java null objects are printed as null in Strings.
Something like this:

words = Hash.new
words[0]="one"
allWords = "all words:"
allWords << words[0]
allWords << words[1]
# --> can't convert nil into String (TypeError)

Is this possible? Or how can I handle nil objects for this case?

5

Ahem, no.

What I'm actually trying is this: I have an array of hashes,
and I like to make strings out of them. Some of the hashes
do not have values for some keys, so when putting together
the string, I get the error message, but I just want to add
"nil" or something else for this case.

···

On 23 Feb., 15:19, Harry <ruby.hardw...@gmail.com> wrote:

Is this what you are looking for?

http://www.rubycentral.com/book/ref_c_hash.html#Hash.new

6

Puh, why do I always forget that /this/ is possible in Ruby.
It's hard to get rid of those "safety handcuffs" ...

Thanks!

7

tchick schrieb:

Is this what you are looking for?

http://www.rubycentral.com/book/ref_c_hash.html#Hash.new

Ahem, no.

Are you sure? See below...

What I'm actually trying is this: I have an array of hashes,
and I like to make strings out of them. Some of the hashes
do not have values for some keys, so when putting together
the string, I get the error message, but I just want to add
"nil" or something else for this case.

   words = Hash.new "nil" # I suppose this is what Harry thought of
   words[0]="one"

   allWords = "all words:"
   allWords << words[0]
   allWords << words[1]

   p allWords # => "all words:onenil"

Regards,
Pit

···

On 23 Feb., 15:19, Harry <ruby.hardw...@gmail.com> wrote:

8

   words = Hash.new "nil" # I suppose this is what Harry thought of

Oh yes, _that's_ good! You're right, I didn't get it the first time!

Thanks.