Asp Forum - Re: Question on IO objects, initialize, and yaml

Eric Hodel

12/11/2006 1:24:00 AM

On Dec 10, 2006, at 12:19 , Mark Noworolski wrote:

> Say I have a class with pseudo code as follows:
> class Test
> def initialize
> @a=1
> @b=File.open("file+Time.now or similar")
> end
> end
>
> Now, imagine that I use this class for a while and then I want to
> dump it to
> a YAML file.
>
> When I restart my code, I want it to read in stuff from the YAML
> file (if it
> exists) and use that as a starting point to work from (basically, I am
> saving state in the yaml file). You'll note that I cannot just do
> this as
> is, because reading in from YAML does not initialize the class, so
> @b would
> not be initialized correctly on restart.

Ruby and YAML provide hooks to cause things to happen when you load
from Marshal or YAML. I think #initialize_copy gets called for
Marshal, I don't know the YAML ones, but they should be easy to find.

> I'd like to just initialize the thing, then read in the YAML file to
> overwrite the state with the saved values. Is there some extremely
> obvious
> ruby way to do this or something equivalent?

Don't do this, use the built-in hooks, that's what they're for.

--
Eric Hodel - drbrain@segment7.net - http://blog.se...

I LIT YOUR GEM ON FIRE!

1 Answer

Mauricio Fernández

12/12/2006 12:08:00 AM

On Mon, Dec 11, 2006 at 02:43:22PM +0900, Mark Noworolski wrote:
> On 12/10/06, Eric Hodel <drbrain@segment7.net> wrote:
> >
> >Ruby and YAML provide hooks to cause things to happen when you load
> >from Marshal or YAML. I think #initialize_copy gets called for
> >Marshal, I don't know the YAML ones, but they should be easy to find.
> >
> I _want_ to use a built-in hook (the ruby way, if you will), if I can figure
> out which one and how to use it.
[...]
> Now, I've experimented with initialize_copy on this code and your
> recommendation, and I cannot get it to do what I want.
>
> Anybody got any other suggestions, or a concrete example for me?
> mark

require 'yaml'
class Foo
def initialize
@foo = 1
@bar = 2
end

def yaml_initialize(tag, val)
end
end

foo = Foo.new
foo # => #<Foo:0xa7dfe614 @bar=2, @foo=1>
YAML.load(YAML.dump(foo)) # => #<Foo:0xa7dfa6e0>

class Foo
def yaml_initialize(tag, val) # !> method redefined; discarding old yaml_initialize
@foo, @bar = val.values_at("foo", "bar")
end
end

YAML.load(YAML.dump(foo)) # => #<Foo:0xa7ddcfc8 @bar=2, @foo=1>

--
Mauricio Fernandez - http://eige... - singular Ruby

comp.lang.ruby

Re: Question on IO objects, initialize, and yaml

Eric Hodel

Mauricio Fernández

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