From: Robert Klemme <bob.news@...>
Date: 2004-08-22T19:30:46+09:00
Subject: Re: Ruby way to update file lines


"Mark Probert" <probertm@nospam-telus.net> schrieb im Newsbeitrag
news:Xns954CA02966DD9probertmnospamtelusn@198.80.55.250...
> "Robert Klemme" <bob.news@gmx.net> wrote in
> news:2opvm8FddmmgU1@uni-berlin.de:
> >
> > They are meant to be constants because they *are* constant.  I just
> > put both variants into a single file but you'll likely need only one
> > of them, don't you?
> >
> When I leave them as constants, Ruby complains with the following error:
>
>   deln.rb:37: dynamic constant assignment
>         COMMENT = lambda {|key, val| "# #{key}:#{val}" }
>                  ^

Then you got the scoping wrong.  Constants should be defined on top level or
class / module scope, otherwise they are of not much use: what do you gain
by reevaluationg and assigning an expression on each method invocation?
That's not what constants are intended for.  You probably did something like
this:

>> def foo() FOO = "bar" end
SyntaxError: compile error
(irb):2: dynamic constant assignment
def foo() FOO = "bar" end
               ^
        from (irb):2

While it should be

FOO = "bar"
def foo() ... end
  # use FOO
or

class Any
  FOO = "bar"
  # use FOO
end

Both of them don't trigger warnings unless you do multiple assignments to
the same constant:

>> FOO = "bar"
=> "bar"
>> FOO = "bar"
(irb):2: warning: already initialized constant FOO
=> "bar"

> In the end, it worked out well.  My code snippet looks like:
>
>             # create a function map for the items we want to delete
>         comment = lambda {|key, val| "# #{key}:#{val}" }
>         delete  = lambda {|key, val| nil }
>         checkmap = {}
>         @nodelist.each do |n|
>             key = "#{n.name}:#{n.ip}"
>             checkmap[key] = (@remove) ? delete : comment
>         end
>
> Where I now have the option of making the deletion permanent or just
> commenting it out.  Which is perfect for my application.

Fine.

    robert