On 11/12/06, David Vallner <david@[...].net>  wrote:
> 
>  Sebastian Reid wrote:
>  > Hi all.
>  >
>  >     I've been working on some Ruby projects using the Rails framework
>  > and getting on well, however recently I've started on some projects
>  > using Ruby alone and have run into some issues as the task gets a little
>  > more complicated.
>  >
>  >     One particular script is giving me trouble and I suspect it is due
>  > to my Perly ways.  Below is a pastebin of the code.  As some I'm sure
>  > can tell, it is an rbot plugin that right now doesn't do a whole lot.
>  >
>  > http://pastebin.com/822611
>  >
>  >     The highlighted line is flagging up the error:
>  >
>  > TypeError: no implicit conversion from nil to integer
>  >
>  >     on line 18 (highlighted).
>  >
>  >     Now this is looking to me like a variable instantiation issue which
>  > brings us back to Perl.  In Perl that line would be perfectly legal
>  > (though some would debate its elegance) and hashes and arrays would be
>  > created as and when required.
>  >
> 
>  In Ruby, only instance variables are autovivified to nil, and that by
>  itself is a behaviour that gets on my nerves (typo-prone).


agreed but see JEGII remark about warnings



From the code it looks @registry should be an object (maybe use a
>  Struct) instead of a Hash, and you should preinitialise its contents to
>  empty arrays and whatnot in its initialize method.


501/2 >  ruby -e 'puts Array.new[nil]'
-e:1:in `[]': no implicit conversion from nil to integer (TypeError)
        from -e:1
Given that I rather think  that
(a) @registry["memory"] is referencing an Array object
and
(b) @registry["context"][1] evaluates to nil

That was the question OP, or was it not?
Now if you really want to shoot yourself into your leg here is the gun:

class  GunArray < Array
       def [] *args, &block
            super(*args,&block) rescue nil end
       end
end


you could also monkeypatch Array but I am too lazy to look if its
method_alias or alias_method ;)

> 
>  >     I'm willing to accept that this may not be the best way to do things
>  > in Ruby, thus I come to you to ask for a quick rundown on best practices
>  > in these situations.
>  >
>  >     I've played around with default procs and the like in the
>  > initialisation routine to no avail.
> 
>  Using blocks to initialize hashes / arrays is fine when not nested,
>  otherwise things get messy. Clean up your data structure initialisation
>  to be explicit?


That is definitely my advice too, but I am less strict ;)

David Vallner
> 
> 
> 
>  Cheers
Robert


-- 
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all progress
depends on the unreasonable man.

- George Bernard Shaw