Singletons and Marshalling

[Charles Hixson]

Does anyone know how singleton's and marshalling interact?

In particular, I want to have my singleton class be able to dump and
load (and be saved on a file). So I'm wondering if there are any
methods to be implemented that would enable this.

In particular, I'm composing a kind of container class that will contain
either an array, a hash, or possibly both of values. Dumping it should
be basically dumping all the members of the hash/array (plus a few
more), and restoring should append the contents of the being-restored
value to the one in memory. (Duplicates aren't a problem as they'll
just be dropped.)

If this can't be done, there are other approaches, but as they involve
things like private class variables & classes that are only used
internally as a cache.... well, the other approach looks cleaner, if
it's possible.

[Austin Ziegler]

I suggest you look at NodeDump; it will handle dumping classes and, I guess,
singleton objects.

-austin
--
austin ziegler * [email]austin@halostatue.ca[/email] * Toronto, ON, Canada
software designer * pragmatic programmer * 2003.11.13
* 23.18.05

[Christoph]

------------
/Christoph

Please send off list mail to
'my_mail@gmy.net'.gsub(/y/,'x')

> -----Original Message-----
> From: Charles Hixson [mailto:charleshixsn@earthlink.net]
> Sent: Friday, 14 November, 2003 04:37 AM
> To: ruby-talk ML
> Subject: Singletons and Marshalling
>
> Does anyone know how singleton's and marshalling interact? Be dumped
>
> In particular, I want to have my singleton class be able to
> dump and load (and be saved on a file). So I'm wondering if
> there are any methods to be implemented that would enable this.
>
> In particular, I'm composing a kind of container class that
> will contain
> either an array, a hash, or possibly both of values.
> Dumping it should
> be basically dumping all the members of the hash/array (plus
> a few more), and restoring should append the contents of the
> being-restored value to the one in memory. (Duplicates
> aren't a problem as they'll just be dropped.)

Since you are - pause - not worried about duplicates, you are
probably talking about pattern singletons? Duplicates, even private
Ones, are sort of bad style in Ruby, since you can easily access the
duplicates with ObjectSpace#each_object - therefore it might
have better to right out outlaw any kind of duplicates, but this
not in keeping with the standard pattern singleton definition
(developed for less dynamic languages).

>
> If this can't be done, there are other approaches, but as
> they involve things like private class variables & classes
> that are only used internally as a cache.... well, the other
> approach looks cleaner, if it's possible.

Here is the marshaling example from (1.8) singleton.rb adopted
to your situation - does this do what you want?

# example
require 'singleton'

class A
include Singleton

def initialize
@hsh = {}
@ary = []
end

def []=(key,val)
@hsh[key]=val
end

def <<(o)
@ary << o
end

private

def _dump(depth = -1)
Marshal.dump([@hsh,@ary,tainted?],depth)
end

def self._load(str)
instance.instance_eval {
h,a,t = *Marshal.load(str)
@hsh.merge h
@ary.concat a
if t
taint
else
untaint
end
}
instance
end

private_class_method :_load
end


/Christoph

[Austin Ziegler]

On Fri, 14 Nov 2003 13:19:04 +0900, Austin Ziegler wrote:

> I suggest you look at NodeDump; it will handle dumping classes and, I
> guess, singleton objects.

I misremembered: NodeWrap.

-austin
--
austin ziegler * [email]austin@halostatue.ca[/email] * Toronto, ON, Canada
software designer * pragmatic programmer * 2003.11.14
* 07.56.16

[Charles Hixson]

That sure *looks* good. It looks as if with only quite minor changes it
will do exactly what I was hoping for.

Christoph wrote:

>------------
>/Christoph
>
>Please send off list mail to
>'my_mail@gmy.net'.gsub(/y/,'x')
>
>
>
>
>

>>-----Original Message-----
>>From: Charles Hixson [mailto:charleshixsn@earthlink.net]
>>Sent: Friday, 14 November, 2003 04:37 AM
>>To: ruby-talk ML
>>Subject: Singletons and Marshalling
>>
>>Does anyone know how singleton's and marshalling interact? Be dumped
>>
>>In particular, I want to have my singleton class be able to
>>dump and load (and be saved on a file). So I'm wondering if
>>there are any methods to be implemented that would enable this.
>>
>>In particular, I'm composing a kind of container class that
>>will contain
>>either an array, a hash, or possibly both of values.
>>Dumping it should
>>be basically dumping all the members of the hash/array (plus
>>a few more), and restoring should append the contents of the
>>being-restored value to the one in memory. (Duplicates
>>aren't a problem as they'll just be dropped.)
>>
>>

>
>Since you are - pause - not worried about duplicates, you are
>probably talking about pattern singletons? Duplicates, even private
>Ones, are sort of bad style in Ruby, since you can easily access the
>duplicates with ObjectSpace#each_object - therefore it might
>have better to right out outlaw any kind of duplicates, but this
>not in keeping with the standard pattern singleton definition
>(developed for less dynamic languages).
>
>
>

>>If this can't be done, there are other approaches, but as
>>they involve things like private class variables & classes
>>that are only used internally as a cache.... well, the other
>>approach looks cleaner, if it's possible.
>>
>>

>
>Here is the marshaling example from (1.8) singleton.rb adopted
>to your situation - does this do what you want?
>
># example
>require 'singleton'
>
>class A
> include Singleton
>
> def initialize
> @hsh = {}
> @ary = []
> end
>
> def []=(key,val)
> @hsh[key]=val
> end
>
> def <<(o)
> @ary << o
> end
>
> private
>
> def _dump(depth = -1)
> Marshal.dump([@hsh,@ary,tainted?],depth)
> end
>
> def self._load(str)
> instance.instance_eval {
> h,a,t = *Marshal.load(str)
> @hsh.merge h
> @ary.concat a
> if t
> taint
> else
> untaint
> end
> }
> instance
> end
>
> private_class_method :_load
>end
>
>
>/Christoph
>
>
>
>
>