TypeList

The TypeList struct provides utilities for dealing with template parameter packs, and in particular is heavily used in the dispatcher and abstractions around the type-based packs to perform compile time logic. Some utilities include concatenating TypeLists, picking out types by index and splitting into separate lists.

TypeListArray

It can also be useful to index into a regular array using the types in a TypeList. This is commonly used in the hydro as a way to abstract the size of the system used depending on runtime options used around MHD/3T physics.

physics/hydro/riemann_solver.hpp:tl-arr

  Prim2Cons<hydro_traits>(vL, UL);
  Prim2Cons<hydro_traits>(vR, UR);
  Prim2Flux<dir1, hydro_traits>(vR, FR);
  Prim2Flux<dir1, hydro_traits>(vL, FL);

physics/hydro/primconsflux.hpp:use-idx

  U(DENS()) = V(DENS());
  Real emag = 0.;
  Real ekin = 0.;
  for (int dir = 0; dir < 3; dir++) {
    U(MOMENTUM(dir)) = V(DENS()) * V(VELOCITY(dir));
    ekin += V(VELOCITY(dir)) * V(VELOCITY(dir));
    if constexpr (hydro_traits::MHD != Mhd::off) {
      U(MAGC(dir)) = V(MAGC(dir));
      emag += V(MAGC(dir)) * V(MAGC(dir));
    }
  }

Types in a TypeList can also be iterated over using the type_for interface together with a templated lambda function.

physics/hydro/riemann_solver.hpp:type_for

  type_for(typename hydro_traits::Conserved(), [&]<typename Vars>(const Vars &) {
    for (int comp = 0; comp < pack.GetSize(Vars()); comp++) {
      auto var = Vars(comp);
      pack.flux(face, var) =
          sRmsLi * (sR * FL(var) - sL * FR(var) + sR * sL * (UR(var) - UL(var)));
    }
  });