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## Versioning

This section describes how the library is prepared for supporting multiple (not backward compatible) changes.

### Template classes

The elements of the library are defined in the `boost::metaparse::v1` namespace. For example the `one_char` class is `boost::metaparse::v1::one_char` and is available after including the `<boost/metaparse/v1/one_char.hpp>` header file.

At the same time the library provides the `<boost/metaparse/one_char.hpp>` header file which includes `<boost/metaparse/v1/one_char.hpp>` and contains the following:

    namespace boost
    {
      namespace metaparse
      {
        using v1::one_char;
      }
    }

This makes it possible to use `one_char` as `boost::metaparse::one_char`.

Future versions of the library may provide other namespaces (eg. `v2`). The header files in `<boost/metaparse/...>` provide the latest version of the library. To always get version `v1`, one should use header files in `<boost/metaparse/v1/...>`.

The library does not use inline namespaces to work on compilers that do not support them.

### Macros

Macros defined by the library are prefixed with `BOOST_METAPARSE_V1_`. For example `BOOST_METAPARSE_V1_STRING`. It is defined in the `<boost/metaparse/v1/string.hpp>` header file. The library provides the `<boost/metaparse/string.hpp>` header file as well, which includes the definition of this macro and provides the following definition:

    #define BOOST_METAPARSE_STRING BOOST_METAPARSE_V1_STRING

This makes it possible to use the macro as `BOOST_METAPARSE_STRING`. Future versions of the library may define other versions of this macro (eg. `BOOST_METAPARSE_V2_STRING`). `BOOST_METAPARSE_STRING` will refer to the latest version.

This versioning does not affect macros that may be overridden by the code using the library. (eg. `BOOST_METAPARSE_LIMIT_STRING_SIZE`)