After talking to Paul and looking at our first crack at the code, it's
starting to become apparent that these two classes ought to be
template-parameter-distinguished versions of the *same* class.
There's just a ton of redundant code otherwise.
What we'd be doing would look something like
template <typename OutputType>
class FEGenericBase {...};
typedef FEGenericBase<Real> FEBase;
typedef FEGenericBase<RealGradient> FEVectorBase;
Which would then allow us to add a default template parameter to FE
giving something like
template <unsigned int Dim, FEFamily T, typename
OutputType=FEGenericBase<OutputOf<T>::type>
class FE : public FEBase {...};
We'd need a few helper metafunctions to get things like
typeof(GradientOf<Real>::type) == typeof(Gradient) correct, so instead of
e.g., dphi being a vector<vector<RealGradient> > in one case and
vec<vec<RealTensor> > in another, we'd have:
std::vector<std::vector<GradientOf<OutputType>::type> > dphi;
And we'd use an if/else metafunction to make sure that data arrays
which only make sense for vector-valued types don't take up any space
in scalar-valued elements:
IfElse<IsVector<T>::value,
std::vector<std::vector<OutputType> >,
NullType> curl_phi;
Thoughts? The main advantage of this design is that it ought to save
us a lot of code copy-and-paste-and-tweak, and may also make some of
the library projection type codes simpler. It would also make it much
easier to add tensor-valued, symmetric-tensor-valued, etc. elements if
people want to do fancy solid mechanics formulations some day.
The main disadvantage is that it would make for uglier FE error
messages in gdb. Only *slightly* uglier, at that - I used the word
"metafunction" above, but anyone familiar with metaprogramming for
PECOS should be reassured that for libMesh I'm talking about simple
idioms like we already have in our numerics/ classes, not any of that
recursive functional compile-time algorithm stuff that produces
eldritch compiler error messages.
---
Roy
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