Instance variable exists?

[Detlef Reichl]

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

 

[SonOfLilit]

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

 

[George Ogata]

Hi Detief, Aur,

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.

 

[SonOfLilit]

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

 

[George Ogata]

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

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.

 

[Giles Bowkett]

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.