Asp Forum - instance_variable_[gs]et

Trans

3/27/2008 4:36:00 AM

Just spinning wheels this evening...

Why does #instance_variable_get/set require an "@" sign in front of
the variable name? It's not like there is any other valid instance
variable name, is there?

And why can't #instance_variable_set take a hash to set more than one
variable at a time?

T.

7 Answers

Florian Gilcher

3/27/2008 12:24:00 PM

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On Mar 27, 2008, at 5:36 AM, Trans wrote:
>
> And why can't #instance_variable_set take a hash to set more than one
> variable at a time?
>
> T.

By the way, if you really need it, it is easily implemented on your own:
Example:

def set_instance_variables(variables)
variables.each do |key, value|
instance_variable_set("@#{key}", value)
end
end

Greetings
Florian
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Trans

3/27/2008 3:29:00 PM

On Mar 27, 8:23 am, Florian Gilcher <f...@andersground.net> wrote:
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>
> On Mar 27, 2008, at 5:36 AM, Trans wrote:
>
>
>
> > And why can't #instance_variable_set take a hash to set more than one
> > variable at a time?
>
> > T.
>
> By the way, if you really need it, it is easily implemented on your own:
> Example:
>
> def set_instance_variables(variables)
> variables.each do |key, value|
> instance_variable_set("@#{key}", value)
> end
> end

Yes, of course. Facets has #instance_assign, but it just seems
wasteful when one method could do.

I don't quite get matz take. How is

variables.each do |key, value|
instance_variable_set("@#{key}", value)
end

cleaner than

instance_variable_set(variables)

T.

Robert Klemme

3/27/2008 7:33:00 PM

On 27.03.2008 16:28, Trans wrote:
>
> On Mar 27, 8:23 am, Florian Gilcher <f...@andersground.net> wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> On Mar 27, 2008, at 5:36 AM, Trans wrote:
>>
>>
>>
>>> And why can't #instance_variable_set take a hash to set more than one
>>> variable at a time?
>>> T.
>> By the way, if you really need it, it is easily implemented on your own:
>> Example:
>>
>> def set_instance_variables(variables)
>> variables.each do |key, value|
>> instance_variable_set("@#{key}", value)
>> end
>> end
>
> Yes, of course. Facets has #instance_assign, but it just seems
> wasteful when one method could do.
>
> I don't quite get matz take. How is
>
> variables.each do |key, value|
> instance_variable_set("@#{key}", value)
> end
>
> cleaner than
>
> instance_variable_set(variables)

How often is that really needed? I can remember only few cases where I
needed that - and those were probably more experimental.

Kind regards

robert

Joel VanderWerf

3/27/2008 8:08:00 PM

Robert Klemme wrote:
> On 27.03.2008 16:28, Trans wrote:
...
>> I don't quite get matz take. How is
>>
>> variables.each do |key, value|
>> instance_variable_set("@#{key}", value)
>> end
>>
>> cleaner than
>>
>> instance_variable_set(variables)
>
> How often is that really needed? I can remember only few cases where I
> needed that - and those were probably more experimental.

I've got a couple of methods in library code I use frequently that
initialize or populate an object from a hash using the loop above. I've
always thought it was kind of a pain (and inefficient) to have to
construct a string for each key.

Why couldn't #instance_variable_set be agnostic about whether you refer
to ivars as "foo" or "@foo" ? I don't see any ambiguity...

--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

Radoslaw Bulat

3/27/2008 10:35:00 PM

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Joel VanderWerf

3/27/2008 11:11:00 PM

Rados3aw Bu3at wrote:
> On Thu, Mar 27, 2008 at 9:07 PM, Joel VanderWerf
> <vjoel@path.berkeley.edu> wrote:
>> I've got a couple of methods in library code I use frequently that
>> initialize or populate an object from a hash using the loop above. I've
>> always thought it was kind of a pain (and inefficient) to have to
>> construct a string for each key.
>
> Does it mean that everyone use/need it? I don't think so.

Don't see what that has to do with anything. There's lots of core
methods that are rarely used. Have you used
Module:protected_method_defined? recently?

>> Why couldn't #instance_variable_set be agnostic about whether you refer
>> to ivars as "foo" or "@foo" ? I don't see any ambiguity...
>
> I don't know if it's main reason but AFAIR Ruby internally use
> instance variables without "@" character to store additional
> information about object (but from Ruby you can't get it).

That's a good point, but my suggestion was for #instance_variable_set to
map both "foo" and "@foo" to the same entry in the table, namely the
entry for "@foo". Hidden entries would remain hidden.

> I think that most important is consistent. We use @ in code and the
> same goes when we want get value by instance_variable_get method.

Maybe.

--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

Eric Hodel

3/28/2008 12:02:00 AM

On Mar 26, 2008, at 21:36 PM, Trans wrote:
> Just spinning wheels this evening...
>
> Why does #instance_variable_get/set require an "@" sign in front of
> the variable name? It's not like there is any other valid instance
> variable name, is there?

There are, but you can only get to them from C.

comp.lang.ruby

instance_variable_[gs]et

Trans

Florian Gilcher

Trans

Robert Klemme

Joel VanderWerf

Radoslaw Bulat

Joel VanderWerf

Eric Hodel

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