Warnings, exceptions, and constant modifications, redux.

[Dumaiu]

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