Re: intuitive concept of iter

[Daniel Kasak <dkasak nusconsulting com au>]

zentara wrote:
> Hi,
> Can anyone explain what an "iter" is?
>
> I see it used in the docs for TextView, TreView, etc,
> indifferent contexts, as if it is some basic entity.
>
> Can someone define what an iter is, and why is it
> so intertwined in the workings of Gtk2?
>
> Are there any real-world analogies?
>
> Thanks
>   
I'll pass on my limited understand of what's going on :)

An iter is an 'iteration' - a single instance in a collection of 
'things'. It's a pointer to a particular instance, that you can use to 
refer to that instance immediately after getting hold of it ( apparently 
it's invalid after anything has happened to the object you're dealing 
with, so you can't hold onto them for any length of time ).

For example, a model for a combo might have 10 'rows' of data. To get a 
pointer to the 1st row, you'd do:

my $iter = $model->get_iter_first

To get the next iter, you'd:

$iter = $model->iter_next($iter)

Or if someone has selected an item in with the combo box, and you want 
to find out what they've selected, you want the 'active' iter ( ie a 
pointer to the row containing the selected data ). So you'd do:

my $iter = $model->get_active_iter

Once you've got the iter ( a pointer to the right 'row' ), you can 
extract data:

my $first_item = $model->get( $iter, 0);
my $second_item = $model->get( $iter, 1);

etc ...

When you come across other objects that use iters, it means that they're 
basically storing & retrieving data in the same way. For example you 
mentioned the TextView - to access characters in a TextView you do 
something like:

my $textbuffer = $textview->get_buffer;
my ( $start_iter, $end_iter ) = $textbuffer->get_bounds;

That gives you pointers to the 1st and last characters. You can then go:

$value = $textbuffer->get_text( $start_iter, $end_iter, 1 );

to get the actual text.

--
Daniel Kasak
IT Developer
NUS Consulting Group
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