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comp.lang.ruby

Variable name to string

reuben doetsch

9/27/2008 10:51:00 PM

[Note: parts of this message were removed to make it a legal post.]

I would like to get the name of the variable in string form, any way this is
possible?

var = 5
puts var.foo #Want this ti put var

i looked into trying to do var.object_id.id2name but some reason this gave
me nil, since if it is bugged or object_id is not returning the correct
object id.

Reuben
4 Answers

Stefan Rusterholz

9/27/2008 11:01:00 PM

0

reuben doetsch wrote:
> I would like to get the name of the variable in string form, any way
> this is
> possible?

No.

> var = 5
> puts var.foo #Want this ti put var

Variables are not objects. Methods operate on objects. Your .foo
operates on 5 (the object your variable 'foo' references), not on 'var'.
For that reason it can't work.

> i looked into trying to do var.object_id.id2name but some reason this
> gave me nil, since if it is bugged or object_id is not returning the correct
> object id.

What should it give you if your object is referenced by multiple
variables?
But it won't work anyway for the above stated reason.

Regards
Stefan
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Chris Shea

9/27/2008 11:34:00 PM

0

On Sep 27, 4:50 pm, reuben doetsch <hjas...@gmail.com> wrote:
> [Note:  parts of this message were removed to make it a legal post.]
>
> I would like to get the name of the variable in string form, any way this is
> possible?
>
> var = 5
> puts var.foo  #Want this ti put var
>
> i looked into trying to do var.object_id.id2name but some reason this gave
> me nil, since if it is bugged or object_id is not returning the correct
> object id.
>
> Reuben

I don't think I quite understand why you need this. But this does
what you're asking for (although, it's a little hacky). See section
8.6 in The Ruby Programming Language by Flanagan and Matz for more.

cms@mvb cat t.rb
class Object
def get_name
line_number = caller[0].split(':')[1].to_i
line_exectued = File.readlines(__FILE__)[line_number-1]
line_exectued.match(/(\S+)\.get_name/)[1]
end
end

abracadabra = 3

puts abracadabra.get_name
cms@mvb ruby t.rb
abracadabra
[~]
cms@mvb


Although, since you're able, apparently, to ask for var.foo, I'd
suggest just putting var in quotes instead of appending '.foo'.

Chris

Lex Williams

9/28/2008 7:37:00 AM

0

but if you write

puts (abracadabra -= 2).get_name

the result won't be the one you're looking for :)
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Brian Candler

9/29/2008 8:24:00 AM

0

reuben doetsch wrote:
> I would like to get the name of the variable in string form, any way
> this is
> possible?
>
> var = 5
> puts var.foo #Want this ti put var

Well, you can do this the other way round:

varname = "foo"
eval("#{varname} = 5")
puts varname

But you almost certainly *don't* want to do this. This is abuse of both
local variables and eval, and it means you're solving the wrong problem,
or solving the problem in the wrong way.

Things you might reasonably do dynamically are:

* invoke methods on an object

obj = "hello"
meth = "upcase"
p obj.send(meth) # "HELLO"

* set and read instance variables of an object

obj = Object.new
ivar = "@foo"
obj.instance_variable_set(ivar, 5)
p obj.instance_variable_get(ivar) # 5

* locate a constant or class by name

klassname = "String"
klass = Object.const_get(klassname)
obj = klass.new
p obj # ""

* add methods in a module to an object

module Foo
def double
self * 2
end
end
obj = "hello"
obj.extend Foo
p obj.double # "hellohello"

* define new methods in a class or an object

Leave this one until you know the language more deeply :-)
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