[/
    Copyright (c) 2022 Dmitry Arkhipov (grisumbras@yandex.ru)

    Distributed under the Boost Software License, Version 1.0. (See accompanying
    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

    Official repository: https://github.com/boostorg/json
]

[/-----------------------------------------------------------------------------]


[section Avoiding physical dependency]

Some users, particularly library authors, may wish to provide conversions
between their types and __value__, but at the same time would prefer to avoid
having their library depend on Boost.JSON. This is possible to achieve with the
help of a few forward declarations.

[doc_forward_conversion_1]

Note that __value_from__ is declared using an out-parameter, rather then
returning its result. This overload is specifically designed for this use-case.

After that the definitions of `tag_invoke` overloads should be provided. These
overloads have to be templates, since __value__ is only forward-declared and
hence is an incomplete type.

[doc_forward_conversion_2]

As discussed previously, we prefer to define a non-throwing overload of
`tag_invoke` for __try_value_to__, rather then the throwing overload for
__value_to__, as the latter can fallback to the former without performance
degradation.

Forward declarations of contextual conversions are done very similarly:

[doc_forward_conversion_3]
[doc_forward_conversion_4]

[endsect]