From: _why <why@...>
Date: 2008-10-07T23:23:10+09:00
Subject: [ruby-core:19164] Re: [Feature #615] "with" operator

On Tue, Oct 07, 2008 at 10:40:16PM +0900, Jim Weirich wrote:
> I think there are two conversations going on in this thread.  The original 
> proposal for 'with' was to allow methods without an explicit object target 
> to be sent to the object designated in the 'with' command.
> 
> The second conversation is about temporarily adding methods to the current 
> object in order to get DSL-like capabilities.  This was thread was 
> introduced by the suggestion of using the mixin/unmixin techniques.

I really think this is a good idea for a `with` method, though.
Rather than altering `self`, we could temporarily re-route methods.
I'm saying that we take mixins a step further: beyond modules and on
to objects, any object at all.

Methods are just messages.  And this would be the interception of
those messages.  Meanwhile, `self` and the ivars aren't messages (in
that one can't manually route them -- you can't "def self".)  And I
think that's what's so surprising about instance_eval, when used as
`with`.  Rather than just routing messages to an object's public
interface, you enter right into its private realm.

Instance eval makes sense when you call it `instance_eval`, but it
sometimes seems surprising when it is masked as something else.

_why