Concepts
========

Concepts and concept utilizing functions.

.. admonition:: Info

   To use declarations from this page, include the ``<essence/concepts.hpp>`` header.

.. cpp:namespace-push:: essence

.. cpp:concept:: template<typename T, typename... Args> anyof

   A concept useful for creating other concepts in which only one of the
   listed types must match.

   **Valid Expressions**

   - ``T`` when ``T`` is any of the types listed in ``Args``.

   .. rubric:: Example

   .. code-block:: cpp

      template<typename T>
      concept stringlike = anyof<T, std::string, std::string_view, const char*, char>;
   
.. cpp:function:: template<typename T, typename... Args> \
                  bool matches(const T& value, const Args&... args)

   Apply the ``==`` operator between ``T`` for each arg in ``args``.
   Each type must be of the same type as ``T``, or of a type that
   passes :cpp:expr:`std::equality_comparable_with`.

   .. rubric:: Example

   .. code-block:: cpp

      if (foo == 1 || foo == 2 || foo == 3 || foo == 4) ;
   
      // The above may be collaped using the `matches` function like so:
      if (matches(foo, 1, 2, 3, 4)) ;

.. cpp:concept:: template<typename T> scannable

   A type that can be scanned with the :cpp:func:`io::scan` and :cpp:func:`io::prompt` functions.

   **Valid Expressions**

   - ``T`` when ``T`` is a :cpp:expr:`char` (:cpp:expr:`std::same_as<T, char>`)
   - ``T`` when ``T`` is an integral type (:cpp:expr:`std::integral<T>`)
   - ``T`` when ``T`` is a floating point type (:cpp:expr:`std::floating_point<T>`)
   - ``T`` when ``T`` is convertible to :cpp:expr:`std::string` (:cpp:expr:`std::convertible_to<T, std::string>`)