On Jul 11, 2013, at 9:57 AM, Martin Owens wrote:
On Thu, 2013-07-11 at 18:40 +0200, jbc.engelen@...2592... wrote:
Which Rects do have area functions? I think it'd be nice to add an area method to the Rect class in 2Geom.
2geom/generic-rect.h:181
There's not just area, but height and width too. I wasn't able to call any of them from the Geom::OptRect objects in the code. Maybe I don't understand what it means by `C foo() const {}` and there is some special way to call it?
One point to keep in mind is that an OptRect differs in that it may or may not be there (thus it is optional). But first I'll do a quick rundown on some of the details of C foo() const {} for the benefit of others on the list.
For a breakdown on that bit of code, we need to look at what it references and the context:
In this case the mentioned method is in a template:
template <typename C> class GenericRect : CoordTraits<C>::RectOps { ...
and is
/** @brief Compute rectangle's area. */ C area() const { return f[X].extent() * f[Y].extent(); }
First is with the comment. The @brief is not really needed as it is ancient Trolltech stuff. The more modern Javadoc approach is that the first sentence is automatically the brief summary. Then again, good comments are the main point in question right now.
So... it's saying it will return some random type that we don't know yet, but decided to call "C" at the moment. C area() const { return f[X].extent() * f[Y].extent(); } ----^
Taking a peek at rect.h, we see class Rect : public GenericRect<Coord>
So that means the generic base template should give the Rect class an effective member of:
Coord area() const {...}
The next part on the base is 'const'
C area() const { return f[X].extent() * f[Y].extent(); } -------------^^^^^
That just says that the member is a const method. That promises that if you call this method it will have no externally visible effect on the instance it is being called from. So if you have a reference or pointer to a const Rect, you can still call this method.
void doSomething(Rect const &target) { Coord block = target.area();
If the method was not marked const, then an attempt to use it there would fail.
However, I'm thinking that you might be having an issue with the "Opt" part of "OptRect". To see if the OptRect contains a value or not, call the isEmpty() method on it. If it is empty, then be sure not to try to use it. Or use the bool operator to test it.
OptRect thing; ...
if (thing) { ????? }
Looking at our conversion cheat-sheet, we can see hints of how to access the underlying rect: http://wiki.inkscape.org/wiki/index.php/CheatSheetForConvertingto2geom
I believe in this case that boost::optional<t> needs to use '*', '->' or 'get()' to access the object... when it is actually present. Thus we see
if (thing) { Geom::Rect other = *thing; Coord block = other.area(); ... }
or
if (thing) { Coord block = thing->area(); ... }