NAME¶
functor - a function wrapper suitable for field expressions
DESCRIPTION¶
A functor is a class-function, i.e. a class that defines the
operator(): it can be used in place of an usual function. Moreover,
functors can be used in Rheolef field expressions, mixed with fields (see
field(2)). For instance, assuming that uh is a field and u_ex is
a functor:
Float err_l1 = integrate (omega, abs(uh - uh_ex), qopt);
where omega denotes a mesh (see geo(2)) and qopt a quadrature
formula (see quadrature_option_type(2)). See also the integrate(4) function.
An usual function u_ex_f cannot always be mixed so nicely in
expressions, due to c++ language rules. For instance, the following
exprtession is valid:
Float err_l1 = integrate (omega, abs(uh - u_ex_f), qopt);
In some case, the compiler cannot build a field expression using usual
functionsn e.g.
Float I = integrate (omega, 0.5*u_ex_f), qopt);
because 0.5*u_ex_f is a direct algebraic operation between usual
functions and flmoating points, that is not defined in the c++ language. A way
to circumvent this difficulty is to convert the usual function into a functor,
as in:
Float I = integrate (omega, 0.5*functor(u_ex_f)), qopt);
IMPLEMENTATION¶
template<class R, class... Args>
std::function<R(Args...)>
functor (R(*f)(Args...)) {
return std::function<R(Args...)>(f);
}