.. Copyright 2022 NWChemEx-Project
..
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.. http://www.apache.org/licenses/LICENSE-2.0
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*****************
Templated Modules
*****************

Our ``CoulombsLaw`` module hard-coded the floating type to ``double``. In
practice we can get a factor of 2 speed-up by using ``float`` instead of
``double``. The trade-off is that ``float`` has reduced precision and is thus
not applicable in all situations. Nonetheless, if we want to support both
``float`` and ``double`` the easiest way to do this is by templating our module
on the floating-point type. To this end, this section looks at how to write a
module ``TemplatedCoulombsLaw``, which is templated on the floating-point type.

.. note::

   In practice, rather than declaring a whole new module
   ``TemplatedCoulombsLaw`` you would probably just modify the ``CoulombsLaw``
   module; however, in order to maintain two separate tutorials we opted to
   create a new module.

Templating slightly changes how the module is declared:

.. literalinclude:: ../../../../tests/cxx/doc_snippets/modules.hpp
   :language: c++
   :lines: 17-20,26-27,32

specifically we need to include a ``template<typename FloatingPointType>``
statement before the call to ``MODULE_RUN``
(``template<class FloatingPointType>`` would work too). The more significant
changes are to the definition of the module where we have to use different
macros: ``TEMPLATED_MODULE_CTOR`` and ``TEMPLATED_MODULE_RUN``. In addition to
taking the name of the module, these macros also take a list of all template
parameters.

.. literalinclude:: ../../../../tests/cxx/doc_snippets/templated_coulombs_law.cpp
   :language: c++
   :lines: 17-21, 38-45,51-54,74-76