From: Eric Mahurin <eric_mahurin@...>
Date: 2005-05-21T23:04:26+09:00
Subject: Re: [ANN] cursor-0.5

--- Simon Strandgaard <neoneye@gmail.com> wrote:
> On 5/20/05, Eric Mahurin <eric_mahurin@yahoo.com> wrote:
> [snip] 
> > Here are the current cursor classes I have:
> [snip]
> 
> Please add a few example files to your package on how to
> use each of these classes.

Sorry, I'll get to that later.  More importantly, I need
examples for the methods.  Here is a example that might be used
in a parser or lexer (my target apps) to give you an idea of
what it can do:

require 'stringio'
# you'll really want something with begin and if
io = StringIO.new("beginififbeginbeginif")
c = Cursor::IO.new(io)
# this would get rid of the seeks - but it has bugs
#c = Cursor::Buffered.new(Cursor::IO.new(io))
loop do
    # see if next 5 chars are "begin" and go back if not
    if c.position?{c.get(5)=="begin"}
        puts('process "begin" here')
    # see if next 2 chars are "if" and go back if not
    elsif c.position?{c.get(2)=="if"}
        puts('process "if" here')
    else
        break
    end
end
raise if !c.eof?

> Your Cursor#get and Cursor#put methods looks a bit longish.

I know, they are not pretty - these methods are quite
overloaded.  The primary advantage of doing this is that many
of methods that use these can get all of this extra
functionality for free.  Take [], []=, each, copy_from,
copy_to, etc. for example.  If I didn't do this, the number of
methods would blow up to get the same functionality.  This is
similar to the overloading done in String#[] for example.

> Having + and - as public methods is maybe dangerous, you
> risk not closing the instances after usage.

The same can be said of succ (used in a Range) and pred.  All
of these methods create "child" cursors that the parent knows
about (with object_id).  The children use their parent to get
their work done.  When the parent closes, it closes all of the
children.  The parent also defines a finalizer for each child
to remove it from its children list.  closing a child is not
really a necessary thing to do - the finalizer will clean
things up.




		
Discover Yahoo! 
Have fun online with music videos, cool games, IM and more. Check it out! 
http://discover.yahoo.com/online.html