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comp.lang.ruby

Does an instance know his own name?

Geoff Barnes

9/4/2006 3:10:00 AM

If a class has built checks and raises an exception if it finds
something wrong, how can I tell which instance had the error? I know
there's an object_id, but can I know the name of the objects own
instance variable?

huey = Nephew.new
duey = Nephew.new
luey = Nephew.new

duey.raise_error_on_purpose_just_for_fun #-> "Nephew 'duey' raised an
error"

Also, can an instance know his 'path' from the top-level?

class Donald

def initialize
@huey = Nephew.new
@duey = Nephew.new
@luey = Nephew.new
end

end

Donald1 = Donald.new
Donald2 = Donald.new

Donald1.huey.raise_error_on_purpose_just_for_fun
#-> "Nephew Donald1.huey raised an error"

Thanks,





--
Posted via http://www.ruby-....
4 Answers

Jeremy Tregunna

9/4/2006 3:59:00 AM

0


On 06-09-03, at 23:10, Geoff Barnes wrote:

> If a class has built checks and raises an exception if it finds
> something wrong, how can I tell which instance had the error? I know
> there's an object_id, but can I know the name of the objects own
> instance variable?

Instances don't have names.

> huey = Nephew.new
> duey = Nephew.new
> luey = Nephew.new

These are examples of binding an instance to a particular key (think
of it in terms of a dictionary/hashtable), and not naming the
instances of Nephew: huey, duey and luey.

--
Jeremy Tregunna
jtregunna@blurgle.ca

Timothy Goddard

9/5/2006 12:25:00 PM

0

You can identify an object by its object_id. Variables are just
references to an object with a convenient name for your use. If you
want to give an object an actual name, you have to pass it in as a
parameter on construction.

Geoff Barnes wrote:
> If a class has built checks and raises an exception if it finds
> something wrong, how can I tell which instance had the error? I know
> there's an object_id, but can I know the name of the objects own
> instance variable?
>
> huey = Nephew.new
> duey = Nephew.new
> luey = Nephew.new
>
> duey.raise_error_on_purpose_just_for_fun #-> "Nephew 'duey' raised an
> error"
>
> Also, can an instance know his 'path' from the top-level?
>
> class Donald
>
> def initialize
> @huey = Nephew.new
> @duey = Nephew.new
> @luey = Nephew.new
> end
>
> end
>
> Donald1 = Donald.new
> Donald2 = Donald.new
>
> Donald1.huey.raise_error_on_purpose_just_for_fun
> #-> "Nephew Donald1.huey raised an error"
>
> Thanks,
>
>
>
>
>
> --
> Posted via http://www.ruby-....

Logan Capaldo

9/5/2006 12:44:00 PM

0


On Sep 5, 2006, at 8:30 AM, Timothy Goddard wrote:

> You can identify an object by its object_id. Variables are just
> references to an object with a convenient name for your use. If you
> want to give an object an actual name, you have to pass it in as a
> parameter on construction.
>
> Geoff Barnes wrote:
>> If a class has built checks and raises an exception if it finds
>> something wrong, how can I tell which instance had the error? I know
>> there's an object_id, but can I know the name of the objects own
>> instance variable?
>>
>> huey = Nephew.new
>> duey = Nephew.new
>> luey = Nephew.new

It is sort of possible to find out someone's name. The following of
course, is easily breakable.
% cat names.rb
class Nephew
def name(&block)
names_objects = eval("local_variables.inject({}){ |h, k| h[k] =
eval(k); h}", block)

names_objects.find { |k, v| v.object_id == object_id }.first
end
end

huey = Nephew.new
duey = Nephew.new
louie = Nephew.new

puts huey.name{}


% ruby names.rb
huey

Gavin Kistner

9/5/2006 3:01:00 PM

0

Geoff Barnes wrote:
> huey = Nephew.new
> duey = Nephew.new
> luey = Nephew.new
>
> duey.raise_error_on_purpose_just_for_fun #-> "Nephew 'duey' raised an
> error"

And what would happen if you did:
huey = Nephew.new
duey = huey
luey = duey
some_array = [ huey ]
huey = nil

duey.raise_error #=> "Nephew...uhm...duey, luey, some_array[ 0
]?...raised an error."

A variable doesn't hold an object, it holds a reference to it. Many
variables (local, global, instance, and class) can all refer to the
same object.

If you have a symbolic name that is unique to an instance, pass that
name in when creating the instance.