**field_functor** - a functor wrapper suitable for field expressions
(obsolete)

This class is now obsolete, from Rheolef version 6.7 and is maintained for
backward compatibility purpose only. Until Rheolef version 6.6, this class was
used to mark functors with profil compatible with fields, i.e. that accepts

**point** as parameter and returns a field value (scalar, vector, tensor).
This mark was used to filter field expression arguments in

**interpolate**
and

**integrate**. From version 6.7, this mark is no more required, and any
function or functor that is callable with a

**point** as argument is valid
in a field expression.

A functor is a class-function, i.e. a class that defines the

**operator()**.
A variable

**f** of a class-function can be used as

**f(arg)** and when
its argument is of type

**point** see point(2), the function

**f**
interprets as a continuous field field. Thus, it can be interpolated see
interpolate(4) and it can be combined within field expressions see field(2)
that appears in arguments of see integrate(4).

struct f : field_functor<f,Float> {
Float operator() (const point& x) const { return 1-norm(x); }
};
// ...
geo omega ("square");
space Xh (omega, "P1");
field fh = interpolate (Xh, f);
test (Xh);
field lh = integrate (f*v);

The current implementation of a

**field_functor** class bases on the
curiously recurring template pattern (CRTP) C++ idiom: the definition of the
class

**f** derives from

**field_functor**<

**f**,Float> that
depend itself upon

**f**. So, be carrefull when using copy-paste, as there
is no checks if you write e.g.

**field_functor**<

**g**,Float> with
another function

**g** instead of

**f**.

template <class Function, class Result>
struct field_functor
: std::unary_function<point_basic<float_traits<Result> >,Result> {
const Function& get_ref() const { return static_cast<const Function&>(*this); }
operator Function() const { return get_ref(); }
Result operator() (const point& x) const { return get_ref().operator()(x); }
};

point(2), interpolate(4), field(2), integrate(4)