From: Mark Hubbart <discord@...>
Date: 2004-04-22T03:58:55+09:00
Subject: Re: yaml doesn't save Proc members


On Apr 21, 2004, at 8:59 AM, Dick Davies wrote:

>
> I'm twiddling around with a dependency tree implementation -
> a bit like rake, but for things like keeping track of what servers
> need shutting down if spamassassin has to bounce for some reason.
>
> It's still very theoretical, but effectively you have a node which
> has
>
> : a name (symbol)
> : a dependency list (array of nodes)
> : a 'users' list (array of nodes which depend on *it*)
> : a block (which gets called to 'resolve' this dependency
>
> I thought I'd bugger about with YAML to save and load the tree,
> but although the arrays all get laid down nicely, the blocks don't.

Ruby pretty much discards the code once it has been compiled; there is 
no way to get it back without re-parsing the script and selecting out 
the original definition.

I would suggest that you might want to store the block/proc as a string 
form the beginning, and eval it when you want the actual block:

block = "{|n| n * 3 }"
(0..5).map &eval("proc " + block)

that way you can store the block in a yaml document, albeit as a string.

> When I call to_yaml, the proc is saved as an empty block,
> and when YAML.load() tries to pull it back, I get:
>
> NoMethodError: allocator undefined for Proc
>     /data/ruby/lib/ruby/1.9/yaml.rb:171:in `load'
>     /data/ruby/lib/ruby/1.9/yaml.rb:171:in `object_maker'
>     /data/ruby/lib/ruby/1.9/yaml/rubytypes.rb:36
>     /data/ruby/lib/ruby/1.9/yaml/rubytypes.rb:34:in `call'
>     /data/ruby/lib/ruby/1.9/yaml.rb:39:in `load'
>     /data/ruby/lib/ruby/1.9/yaml.rb:39:in `load'
>     test/fuct_test_knot_yaml.rb:55:in `test_yaml_block'
>
> So I guess I need another way to attach behaviour to a node...
> would singleton methods have the same problem ?
>  I'm not big on inheritance....
>
> -- 
> I don't like spinach, and I'm glad I don't, because if I
> liked it I'd eat it, and I just hate it.
> 		-- Clarence Darrow
> Rasputin :: Jack of All Trades - Master of Nuns
>