From: Robert Klemme <shortcutter@...>
Date: 2007-09-20T06:00:03+09:00
Subject: Re: exceptions and eval'ing a string

On 19.09.2007 19:44, Chris Hall wrote:
> Here's my situation
> 
> 
> I have a setup such as:
> 
> ----task.rb----
> class Task
>   def initialize(name, &action)
>     @name = name
>     @action = action
>   end
> 
>   def run
>     @action.call(self)
>   end
> end
> 
> ----task_runner.rb----
> require 'task'
> 
> t = Task.new('task_1') { |t| puts t.name }
> t.run # => thing
> 
> 
> what i am now trying to do is put the Task creation code inside a file
> and eval that as a string
> 
> ----thing.task----
> Task.new('task_1') P |t| puts t.name }
                      ^
I'd say you get a syntax error here.

> ----task_runner.rb----
> require 'task'
> def load_task
>   @t = eval('thing.task')
> end
> 
> @t = nil
> load_task
> @t.run
> 
> and this works...however, the difference is that if an exception is
> thrown as part of the Task's action (when it is run) eval craps out with
> an exception like
> 
> (eval):15

That statement seems illogical, because eval is only used for loading 
the task but you claim that eval throws during execution of the task. 
What am I missing here?

> and it brings down the entire script, which is a bad thing because i'm
> running each task in a thread.  this doesn't happen obviously when i'm
> not eval'ing.
> 
> can someone explain to me what is going on?  I'm thinking it's a
> scoping/context thing, but i'm not really sure.

Personally I dislike the way you use instance variables here.  Why don't 
you just let load_task return the new Task and assign the result to a 
local variable?

Kind regards

	robert