Instance variable exists?

Ruby
1

Hi,

what is the preferred way to see if an object already includes a
instance variable?

for now i do something like:

@my_object.instance_variables.include? “var_name”

Cheers
detlef

2

Hi,

AFAIK it’s the only way.

Question: Why does Object#instance_varialbe_get have no documentation?
It’s behaviour isn’t that clear in cases like

3

Hi Detief, Aur,

On 2/19/07, SonOfLilit [email protected] wrote:

Hi,

AFAIK it’s the only way.

There’s also:

obj.instance_eval{defined?(@foo)}

As you’re hopefully aware, though, it’s probably not particularly
straightforward because it’s discouraged in general. Peeking at an
object’s instance variables is kinda intruding on its privacy. There
are some valid uses to be sure, but usually I think you’re better off
providing accessors for anything of interest outside the object.

Question: Why does Object#instance_varialbe_get have no documentation?
It’s behaviour isn’t that clear in cases like

Where are you looking? “ri instance_variable_get” gives me docs.

Regards,
George.

4

On 2/19/07, SonOfLilit [email protected] wrote:

aur-sarafs-computer:~ aursaraf$ ri Object#instance_variable_get -T
------------------------------------------- Object#instance_variable_get
instance_variable_get(ivarname)

 (no description...)

aur-sarafs-computer:~ aursaraf$ ruby -v
ruby 1.8.5 (2006-12-04 patchlevel 2) [i686-darwin8.8.1]

g@bang:~$ ri -T instance_variable_get
------------------------------------------- Object#instance_variable_get
obj.instance_variable_get(symbol) => obj

 Returns the value of the given instance variable (or throws a
 NameError exception). The @ part of the variable name should be
 included for regular instance variables

    class Fred
      def initialize(p1, p2)
        @a, @b = p1, p2
      end
    end
    fred = Fred.new('cat', 99)
    fred.instance_variable_get(:@a)    #=> "cat"
    fred.instance_variable_get("@b")   #=> 99

g@bang:~$ ruby -v
ruby 1.8.5 (2006-12-25 patchlevel 12) [i686-linux]

Maybe a version thing? (Just guessing.)

Regards,
George.

5

aur-sarafs-computer:~ aursaraf$ ri Object#instance_variable_get -T
------------------------------------------- Object#instance_variable_get
instance_variable_get(ivarname)

 (no description...)

aur-sarafs-computer:~ aursaraf$ ruby -v
ruby 1.8.5 (2006-12-04 patchlevel 2) [i686-darwin8.8.1]

6

Rdoc is there !!

ri instance_variable_get
------------------------------------------- Object#instance_variable_get
obj.instance_variable_get(symbol) => obj

 Returns the value of the given instance variable (or throws a
 +NameError+ exception). The +@+ part of the variable name should be
 included for regular instance variables

    class Fred
      def initialize(p1, p2)
        @a, @b = p1, p2
      end
    end
    fred = Fred.new('cat', 99)
    fred.instance_variable_get(:@a)    #=> "cat"
    fred.instance_variable_get("@b")   #=> 99
7

On 2/18/07, SonOfLilit [email protected] wrote:

straightforward because it’s discouraged in general. Peeking at an
object’s instance variables is kinda intruding on its privacy. There
are some valid uses to be sure, but usually I think you’re better off
providing accessors for anything of interest outside the object.

Question: Why does Object#instance_varialbe_get have no documentation?
It’s behaviour isn’t that clear in cases like

Where are you looking? “ri instance_variable_get” gives me docs.

FYI I get the same thing.
E:\Documents and Settings\Jason>ri instance_variable_get
------------------------------------------- Object#instance_variable_get
instance_variable_get(ivarname)

 (no description...)

E:\Documents and Settings\Jason>ruby -v
ruby 1.8.5 (2006-08-25) [i386-mswin32]

documentation here:
http://www.ruby-doc.org/core/classes/Object.src/M000323.html

8

FYI I get the same thing.
E:\Documents and Settings\Jason>ri instance_variable_get
------------------------------------------- Object#instance_variable_get
instance_variable_get(ivarname)

 (no description...)

E:\Documents and Settings\Jason>ruby -v
ruby 1.8.5 (2006-08-25) [i386-mswin32]

same here:

giles-computer:giles [02-18 08:00] ~
! ri Object#instance_variable_get -T
------------------------------------------- Object#instance_variable_get
instance_variable_get(ivarname)

 (no description...)

giles-computer:giles [02-18 08:00] ~
! ruby -v
ruby 1.8.5 (2006-08-25) [i686-darwin8.8.3]

haven’t had any trouble with ri on this machine before, that I remember.