Re: [boost] advice needed for Boost.svg_plot

From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2007-07-04 06:29:41

Jake Voytko wrote:
>   plot_range(my_plot, data.begin(), data.end(),
>                   default_functor, human_age,
>                   circle,
>                   orange, red,
>                   3, 10);

It would be great to be able to write just 'data' in place of 
'data.begin(), data.end()'.  Is there anything stopping this?

I hope that in typical usage it will automatically choose a plot style 
(and I would vote for allocating colours in 'resistor colour code 
order', though starting with brown is not often a popular choice).

Presumably the two functors are to extract the X and Y values from the 
object.  Having 'x' and 'y' in the names would make this clear, if this 
is the case.  I would be interested to see how the various lambda 
techniques could be used to write these functors inline.  Presumably in 
the case where the data is a sequence of numeric values the functor is 
unnecessary.  In particular, I would hope that a sequence<numeric> 
would use the index as X (starting at 0 or 1?), and the value as Y, and 
container<std::pair<numeric,numeric>> would use pair.first as X and 
pair.second as Y.  Right?  (There are plenty of C++ users (though not 
on this list) who would be put off by the concept of functors, and who 
would benefit from having it 'just work').

So hopefully in many cases it reduces to:

   plot_range(my_plot, data);

which I certainly find acceptable without any extra magic.

When you do need to use more non-default parameters, I think that I 
would use a style object like this:

   plot_range(my_plot, data, plot_style(red, circle));

Since the types for the colours and point shapes are distinct you can 
save the user from having to remember a correct order by providing 
plot_style constructors with both parameter orderings.  This can extend 
to the stroke width.  But there is a problem with the fill colour; what 
is that?  Is it for the area under the curve?  Why would you want it to 
be different from the stroke colour?  - and also for the 'size'; what 
is that?, because they are not distinct.

Boost.Parameter does a good job when large numbers of parameters are 
unavoidable.  Do check on the comprehensibility of error messages and 
the compile time increase, as these are the most common problems (IMO) 
with 'advanced' things like Boost.Parameter.

Regards,

Phil.