On Tue, 12 Jun 2012, John Peterson wrote:
>> template <typename OutputType>
>> class FEGenericBase {...};
>>
>> typedef FEGenericBase<Real> FEBase;
>> typedef FEGenericBase<RealGradient> FEVectorBase;
>
> Urk... I guess my own preference would have been for *fewer* templates
> in the FE hierarchy rather than more,
Mine too, trust me. My first forays into libMesh were delayed by my
difficulty figuring out the FE templating tricks...
> but if you say this is a good design I trust your judgment.
I think it's the best we can do in C++. We really want a ton of
common non-cut-n-pasted code between the vector and scalar FE classes,
we don't want the gross inefficiencies (and backwards compatibility
breakage) implied by a runtime polymorphic design, and so that leaves
us with templates.
> Also, it might be handy if we could keep using the equivalent of
> FEBase::build() in the new system... if the base class is templated,
> does this functionality become trickier to implement?
Slightly. FEBase::build() will only work if you know you're asking
for a scalar FE type, likewise for FEVectorBase::build() and vector
types. FEAbstract::build() will work for either, but will give a
higher-level base class without the output-type-specific
functionality. And we'll have something like "bool
FEAbstract::rank()" (returning 0 for scalar, 1 for vector, etc) for
cases where your code really needs the output-type-specific
functionality but doesn't know a priori which output type code path
it's going to have to go down for a given FE type.
>> 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 {...};
>
> Hmm, so then FE is *not* derived from this new FEGenericBase class at
> all, but rather an untemplated FEBase class, similar to what we have
> now?
No, I was just typing too fast. Trying again:
template <unsigned int Dim, FEFamily T, typename
OutputType=FEGenericBase<OutputOf<T>::type>
class FE : public FEGenericBase<OutputType> {...};
---
Roy
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