.. _file_include_match.hpp:

File match.hpp
==============

|exhale_lsh| :ref:`Parent directory <dir_include>` (``include``)

.. |exhale_lsh| unicode:: U+021B0 .. UPWARDS ARROW WITH TIP LEFTWARDS



Compile-time key -> type matcher (first-match wins). 



.. contents:: Contents
   :local:
   :backlinks: none

Definition (``include/match.hpp``)
----------------------------------


.. toctree::
   :maxdepth: 1

   program_listing_file_include_match.hpp.rst



Detailed Description
--------------------

Provides a tiny pattern-matching facility that selects a type based on a compile-time key. You declare alternatives with ``case_<K, T>`` and an optional ``default_<T>``. The alias ``match_t<Key, Alts...>`` yields the selected ``T``.


Example

usingA=structA_;
usingB=structB_;
usingD=structD_;

//PicksBbecauseKey=='b'matchesthesecondcase.
usingR=:ref:`exhale_typedef_match_8hpp_1a7e43839f4a7b91a68bb27d983e8b7ed4`<'b',
:ref:`exhale_struct_structctql_1_1case__`<'a',A>,
:ref:`exhale_struct_structctql_1_1case__`<'b',B>,
:ref:`exhale_struct_structctql_1_1default__`>;
static_assert(std::is_same_v<R,B>);

//Ifnocasematchesandnodefault_isprovided,resultisvoid:
usingR2=:ref:`exhale_typedef_match_8hpp_1a7e43839f4a7b91a68bb27d983e8b7ed4`>;
static_assert(std::is_void_v<R2>);


Keys are compared with ``==`` at compile time. This works for integral, enum, and other literal NTTPs that support ``constexpr`` equality. 







Includes
--------


- ``type_traits``



Included By
-----------


- :ref:`file_include_predicates.hpp`




Namespaces
----------


- :ref:`namespace_ctql`


Classes
-------


- :ref:`exhale_struct_structctql_1_1case__`

- :ref:`exhale_struct_structctql_1_1default__`


Typedefs
--------


- :ref:`exhale_typedef_match_8hpp_1a7e43839f4a7b91a68bb27d983e8b7ed4`