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#################
Writing a Visitor
#################

To avoid assuming a particular set of operations WTF relies on the visitor
pattern. This page should eventually be a tutorial, but for now is just a set
of notes.

Assume that ``visitor`` is an object of type ``T``. The dispatch function will
additionally require a ``std::tuple<FPList...>`` where ``FPList...`` is a list
of the floating-point types you want to be able to support. Then assume we are
trying to dispatch based on the wrapped types of ``N`` ``FloatBuffer`` objects.

- ``T`` must be a callable type, i.e., define ``operator()``. Functions,
  lambdas, and functors all satisfy this criterion
- ``operator()`` may be overloaded. If it is overloaded, the usual C++ overload
   resolution rules will be used to select the appropriate overload.
- Dispatching considers the type of the floating point buffers and the number of
   floating point buffers.
- ``operator()`` overloads must accent ``N`` parameters.
- ``operator()`` must possess an overload capable of supporting any permutation
  with replacement of the types in ``FPLists...``.

  - The easiest way to satisfy this is to have a templated overload with ``N``
    template parameters (one for the type of each positional argument).

- Each ``FloatBuffer`` will be unwrapped to a ``std::span<U>`` object where
  ``U`` is the type of the wrapped floating point objects.