The previous (and only) overload of choose_parameter required two parameters,
with the default parameter often being a default constructed object
of type the type of the object being passed in named parameter.
For example:
typedef typename CGAL::GetPointMap<PointRange, NamedParameters>::type Point_map;
Point_map pm = choose_parameter(get_parameter(np, internal_np::point_map),
Point_map());
However, this can be unpleasant, for example when passing functors that have
an underlying lambda such (function_property_map, ...) because lambdas
cannot be default constructed.
With the new API:
typedef typename CGAL::GetPointMap<PointRange, NamedParameters>::type Point_map;
Point_map pm = choose_parameter<Point_map>(get_parameter(np, internal_np::point_map));
all is well.