From: Robert Klemme <shortcutter@...>
Date: 2010-09-23T00:41:02+09:00
Subject: Re: temporarily override instance variable in a block

On Tue, Sep 21, 2010 at 7:06 PM, Jean-denis Vauguet <jd@vauguet.fr> wrote:

> I strived to override instance variable on a per-block basis, but I'm
> not satisfied with my results. Here's a snippet:
> http://gist.github.com/589924
>
> The goal is: execute a block but have it use a different value for a
> previously defined instance variable, all of this in the context of a
> class instance (the instance variable belongs to this class instance).
>
> Two approach are illustrated: variable swapping and instance_eval. The
> former does the trick but it's cumbersome and not thread-safe.

Exchanging instance variable values is _never_ thread safe - unless
you take extra measures (synchronization).

> The latter, I don't understand why, fails, for the block seems to be called
> in the

?  Your second approach does not actually swap values of an instance
variable but tries to create a copy of the instance and work with
that.  This has vastly different properties (apart from that it may
not work for certain types of objects as Brian said): in cases you
risk losing modifications on the copy.

I completely agree with Brian: please provide more background.

Kind regards

robert

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