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42 lines
1.4 KiB
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42 lines
1.4 KiB
Plaintext
[/
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Copyright (c) 2022 Dmitry Arkhipov (grisumbras@yandex.ru)
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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Official repository: https://github.com/boostorg/json
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]
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[/-----------------------------------------------------------------------------]
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[section Avoiding physical dependency]
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Some users, particularly library authors, may wish to provide conversions
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between their types and __value__, but at the same time would prefer to avoid
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having their library depend on Boost.JSON. This is possible to achieve with the
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help of a few forward declarations.
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[doc_forward_conversion_1]
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Note that __value_from__ is declared using an out-parameter, rather then
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returning its result. This overload is specifically designed for this use-case.
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After that the definitions of `tag_invoke` overloads should be provided. These
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overloads have to be templates, since __value__ is only forward-declared and
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hence is an incomplete type.
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[doc_forward_conversion_2]
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As discussed previously, we prefer to define a non-throwing overload of
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`tag_invoke` for __try_value_to__, rather then the throwing overload for
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__value_to__, as the latter can fallback to the former without performance
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degradation.
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Forward declarations of contextual conversions are done very similarly:
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[doc_forward_conversion_3]
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[doc_forward_conversion_4]
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[endsect]
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