Re: [boost] [gil::io] Feedback for scanline_read_iterator

Subject: Re: [boost] [gil::io] Feedback for scanline_read_iterator
From: Nathan Ridge (zeratul976_at_[hidden])
Date: 2013-02-18 15:56:00

> > I imagine your line-by-line reading iterator would look something like
> > (PSEUDO-CODE!!!):
> >
> >
> > class line_by_line_iterator {
> > buffer_t& buffer;
> >
> > public:
> > const buffer_t& operator*() const { return buffer; }
> > void operator++() { format_specific_read_one_line_into(buffer); }
> > };
> >
> >
> > I'd do it using iterator_facade.
> >
> > A case that this fails to manage efficiently is when your format-specific
> > implementation has an efficient way to skip forward without actually
> > decoding. This is not something that I've ever had to worry about, but I
> > think you could do it easily enough by adding a flag and doing the read
> > lazily in operator*.
>
> you mean pass a boolean into operator*?

Surely not, as the signature of an overloaded operator is fixed :)

I think Phil means rather than do the read in operator++, just set a flag
in operator++ that the read should be done, and actually do it in
operator* (which then clears the flag). Then if someone calls operator++ 
again without calling operator* (which you can detect by the flag being 
set in operator++), you can do a skip in operator++, and thus avoid 
decoding the line you didn't need.

Regards,
Nate