Instance_variable_et

Ruby
1

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.

2

Hi,

In message “Re: instance_variable_[gs]et”
on Thu, 27 Mar 2008 13:36:23 +0900, Trans [email protected]
writes:

|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?

Because it’s part of a method name.

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

I don’t think it makes programs cleaner.

          matz.
3

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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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4

On Mar 27, 8:23 am, Florian G. [email protected] wrote:

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.

5

On Mar 27, 12:43 am, Yukihiro M. [email protected] wrote:

Hi,

In message “Re: instance_variable_[gs]et”
on Thu, 27 Mar 2008 13:36:23 +0900, Trans [email protected] writes:

|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?

Because it’s part of a method name.

Sorry matz, I don’t follow. What is “it” and what method name?

T.

6

On 27.03.2008 16:28, Trans wrote:

variable at a time?
Yes, of course. Facets has #instance_assign, but it just seems
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

7

Robert K. wrote:

On 27.03.2008 16:28, Trans wrote:
…
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…

8

On Thu, Mar 27, 2008 at 4:28 PM, Trans [email protected] 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)

It won’t but he didn’t say that. And Florian G. showed you that
you can write your own method that do it for you. I don’t think that
Ruby should have built-in such a method. Using
instance_variable_[sg]et should be very rare (for example in
metaprogramming) and using such a loop even more.

–
Rados³aw Bu³at

http://radarek.jogger.pl - mój blog

9

Rados³aw Bu³at wrote:

On Thu, Mar 27, 2008 at 9:07 PM, Joel VanderWerf
[email protected] 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.

10

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.

11

On Thu, Mar 27, 2008 at 9:07 PM, Joel VanderWerf
[email protected] 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.

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).

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.

–
Rados³aw Bu³at

http://radarek.jogger.pl - mój blog

12

2008/3/27 Rados³aw Bu³at [email protected]:

instance_variable_set(variables)

It won’t but he didn’t say that. And Florian G. showed you that
you can write your own method that do it for you. I don’t think that
Ruby should have built-in such a method. Using
instance_variable_[sg]et should be very rare (for example in
metaprogramming) and using such a loop even more.
As a DSL implementor I could not disagree more with you, obviously
there are many people who wrote the same code
each { |k,v|
ivar_set “@#{k}”, v

that would mean that it would be a nice feature to have, it would
simply be the most DRY solution to the problem (or DROP in this case).

Cheers
Robert

http://ruby-smalltalk.blogspot.com/

Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein