Asp Forum - Re: [ANN] cursor-0.5

Eric Mahurin

5/21/2005 2:04:00 PM

--- 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.

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Re: [ANN] cursor-0.5

Eric Mahurin

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