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``static_assert``
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Notice that we can create an ``Array<std::string>``---but that's really not our intent,
and we are likely going to do things that only make sense with numbers.

.. code:: c++

   Array<std::string> x(5, 5, "x");

We can add a ``static_assert`` to disallow this---a static assert is evaluated at compile time.
Just instead of our ``Array`` constructor, we just add:

.. code:: c++

   static_assert (std::is_arithmetic_v<T>);

This ensures that ``T`` is an arithmetic type (integer or floating point type).

.. note::

   This is defined in ``<type_traits>``

There are additional type checks like ``is_integral_v`` and ``is_floating_point_v``

.. tip::

   The ``_v`` versions of these checks were introduced in C++17.  You may need to compile
   as:

   .. prompt:: bash

      g++ -std=c++17 ...

   For C++11, you would do:

   .. code:: c++

      static_assert (std::is_arithmetic<T>::value);