On Sat, Aug 08, 2009 at 01:14:53PM +0200, Werner Smekal wrote:
> Hi Arjen,
>
> >>
> >> While I like the API simplification this could provide, I have two
> >> primary concerns:
> >>
> >> First, could the first argument - the field to get/set - be an
> >> enumerated type of some sort? This should help catch typos at
> >> compile
> >> time rather than run time. (PL_LINE_WIDTH rather than "line width").
> >> Additional fields would then require adding elements to the
> >> enumeration which, as I understand, should not break existing code.
>
> Yes, enumeration of #define macros would be much better and faster.
> Comparing strings is surely not the best.
> >>
> >> Second, the void* approach may not translate well to other languages.
> >> I'm not sure if there is a way to do this in C that would translate
> >> well to the other PLplot-supported languages though.
> >>
> >
> > I agree that a void * argument would be very bad for most languages,
> > if not all, and it leaves the interpretation of the value up to the
> > programmer. What about filling a structure instead?
>
> Or even better an union. It's always problematic how such things
> should be solved, but I even have another idea. Why not get ALL
> information in one struct. e.g.
>
> plgetattr( struct plAttributes* att);
>
> struct plAttributes {
> int width;
> int frontcolor;
> int backcolor;
> ......
> }
>
> You will not use such functions in critical situations anyway (or?),
> so speed is not a problem and you could get all attributes at once. On
> the other side, maybe difficult to port to other functions, but
> something like structs or tables all languages have, or?
The big downside of this is that every time you add a new function
you have to change the structure which is formally an API change (as
opposed to just an API addition).
Not all languages have structures. For example in f77 you end up resorting
to common blocks or other such ills.
I would suggest something like
plgvarf(int varid, PLFLT * val)
where varid is the #defined id of the variable to get. You could make enums
of these in languages which support them. val is the returned value. Almost
all of the get functions will return a PLFLT. For those where a int or
string is returned we could have
plgvari(int varid, int * val)
plgvarc(int varid, char ** val)
This maintains all typechecking on the returned value and avoid void *. It will
also be easily ported to all other languages.
Where this more messy than the current approach is where you want to get a
set of returned values (e.g. plgvpw returned viewport limits - 4 numbers).
I don't know if there is a good generic solution to this.
Andrew
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