From: Dumaiu <Dymaio@...>
Date: 2007-12-02T13:34:59+09:00
Subject: Warnings, exceptions, and constant modifications, redux.

	Hello, all.  With your permission I'd like to resurrect a topic that
seems to have died in 2002.  At least, this is the most info I've
found.  The question was, Why does modification of a constant produce
a warning and not an exception?  Matz's answer, ruby-talk 48168, was
as follows (angle brackets added):

> Hi,
>
> In message "warning modifying constant & 'global constant'"
>     on 02/08/26, David Garamond <davegaramond / icqmail.com> writes:
>
> |1. if someone attempts to modify a constant, why does ruby choose to
> |emit a warning instead of a fatal error?
>
> If it is a fatal error, something like Ruby embedded editor will meet
> serious problems, e.g.
>
>   M-x eval-ruby-expression
>   Eval: Foo = 42<ret>
>   bang!
>
> |2. is there a beast called a 'global constant'? i tried defining $Foo
> |and ruby allows me to rebind $Foo later.
>
> No.  $Foo is a plain global variable.
>
>	 							matz.

Unfortunately, I'm not familiar with 'eval-ruby-expression', which
looks like some sort of Emacs command.  So I still consider it a
fairly serious problem that modification of a constant produces
nothing more serious than a warning, which is useless without human
supervision.  Especially because, even if an exception were raised
instead, a bypass system is still so easy to arrange:

	class Module
		def const_set!( name, val )
			remove_const(name) if const_defined?(name)
			const_set( name, val )
		end
	end

Is this 'embedded editor' problem the same as it was five years ago?
Could somebody who *does* know about embedded editors explain what it
is about them that makes constants so hard to deal with?  Ruby-talk
48271, from the same thread:

> Hi,
>
> In message "Re: warning modifying constant & 'global constant'"
>     on 02/08/27, Paul Brannan <pbrannan / atdesk.com> writes:
>
> |>   M-x eval-ruby-expression
> |>   Eval: Foo = 42<ret>
> |>   bang!
> |
> |What problems would there be with making it an exception?
>
> for example, eval-current-buffer may cause trouble if it redefines
> contants.
>
>	 							matz.

How do embedded editors normally handle exceptions?
	Thanks to David Garamond for creating the prior thread.



	- Jonathan