[eigen] Map & TensorMap and setData() functionality

[Gabriel <gnuetzi@xxxxxxxxx>]

Why is there no functionality for


Map<EigenType> a(ptr);

a->setData(otherPtr);


That would be helpful, if we want to store a mapping expression 
somewhere and change the data ptr around.

Of course so far this is not possible, but we always need to do this to 
somehow mimic this

a = Map<EigenType>(otherPtr);

Is there a reason for not setData() functionality?

The same would apply for TensorMap, where a setData function would even 
be more efficient since the constructor always needs an DSize 
(dimension) array...?

a = TensorMap(otherPtr, dimensions);

I think miss something here ? :)

BR Gabriel