Re: [boost] A design for geometric objects

Subject: Re: [boost] A design for geometric objects
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2008-11-15 21:06:00

Steven Watanabe wrote:

> Wait.  How does that work:
> 
> Right triangle models Triangle.
> Equilateral triangle models Triangle.
> Therefore, right triangle can be converted to equilateral triangle?

Actually I meant only the concept it directly models, not the ones which 
are indirectly so.
A model of Right triangle can be constructed from any model of Right 
triangle, but not from a model of Triangle.

The idea is to be able to have similar mechanisms to that of 
containers/ranges with adaptors, such as this example:

SomeContainer a = transform(some_range, some_function);
(actually you have to write
SomeContainer a(
     begin(transform(some_range, some_function)),
     end(transform(some_range, some_function))
);)

with transform = make_transform_range from Boost.RangeEx.

This results in something fairly equivalent to

SomeContainer a;
std::transform(
     some_range.begin(), some_range.end(),
     std::back_inserter(a),
     some_function
);

Maybe it shouldn't be required however. For ranges which are proxies or 
adaptors it makes little sense to be able to be constructed from any range.