CFD Online Discussion Forums - Convert templated class into vector

Quote:

Originally Posted by Peter Müller (Post 366414)

Hello together

First sorry for creating a new thread but I could not find what I was looking for.

I'm creating a new boundary and the boundary should be build up as templated version so to make it usable for any kind of quantity. The problem now is that I would like to do a coordinate transform to the velocity.
Therefore I need to grab the internal field like

Field<Type> iField = this->internalField();

In a next step I wanted to create a vectorField if "Type" is vector

if(pTraits<Type>::rank ==1)
{
Field<vector> myField = iField;
}

As you may probably already notice this want work since iField is templated so it can't be given to a vector field since the compiler doesn't know that my if-statement only allows the operation if Type==vector.

Has anybody an idea how to circumvent this problem?

Many thanks
Peter

You are correct. Since things are templated, you would normally not like that. What you need is a template specialization for the type vector that implements what you want. If you haven't worked with this before, it may take you a few attempts to get it going. The important points:

The template specialization itself must be defined within a namespace.
The template specialization must be seen before the generic template form.

A trivial example can be see in the OPENFOAM UList<T> implementation. Take a look at the [] operator (the const implementation).
From the UList.H:

Code:

 

inline const T& operator[](const label) const;

Within UListI.H, you will find the specialization and the generic form:

Code:

 

namespace Foam

{

    // Template specialization for bool

    template<>

    inline const bool& Foam::UList<bool>::operator[](const label i) const

    {

    ...

    }

} // end of namespace Foam

 

// const element access

template<class T>

inline const T& Foam::UList<T>::operator[](const label i) const

{

...

}

In your particular case, you can either specialize the entire method for various vector, or factor it out as a private method. In either case, you can view the specialization as being a compile-time version of an 'if' or a 'switch'.

I hope this helps you get going.