= Extension Modules

This library can also be used to https://www.sqlite.org/loadext.html::[run-time loadable extensions]
that can be used by other applications, e.g. the `sqlite3` CLI.

In order to write this, you'll need to include `boost/sqlite/extension.hpp`,
and write a named module like so:

[source,cpp]
----
BOOST_SQLITE_EXTENSION(testlibrary, conn)
{
  // create a function that can be used in the plugin
  create_scalar_function(
    conn, "assert",
    [](boost::sqlite::context<>, boost::span<boost::sqlite::value, 1u> sp)
    {
        if (sp.front().get_int() == 0)
          throw std::logic_error("assertion failed");
    });
}
----

[source,sqlite]
----
SELECT load_extension('./test_library');

select assert((3 * 4) = 12);
----

In order to build this, you'll to link against `Boost::sqlite_ext`
instead of `Boost::sqlite`.

Including the `extension.hpp` header will also define
`BOOST_SQLITE_COMPILE_EXTENSION`, which will include `sqlite3ext.h`
instead of `sqlite3.h` and create an inline namespace `ext` inside
`boost::sqlite`.

This prevents linker issues, but will not allow you to mix extension
and non-extension code in one translation unit.