////
Copyright (c) 2023 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
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= Direct Conversion
For large inputs parsing into the library's containers followed by conversion
via <<ref_value_to>> (or vice versa <<ref_value_from>> followed by
serialization from a <<ref_value>>) might be prohibitively expensive. For these
cases the library provides components that allow parsing directly into and
serializing directly from user-provided objects.

The drawback of this approach is that fully custom type representations are
not supported, only the library-provided conversions are. Also all objects that
should be populated by parsing have to be default constructible types. This
includes not only the top-level object, but e.g. elements of containers,
members of described `struct`s, and alternatives of variants.

That being said, if your types are default-constructible and you don't need the
customisability allowed by <<ref_value_to>> and <<ref_value_from>>, then you
can get a significant performance boost with direct conversions.

Direct parsing is performed by the <<ref_parse_into>> family of functions. The
library provides overloads that take either <<ref_string_view>> or
`std::istream`, and can report errors either via throwing exceptions or setting
an error code.

[source]
----
include::../../../test/snippets.cpp[tag=doc_parse_into_1,indent=0]
----

If you need to combine incremental parsing with direct parsing, you can resort
to <<ref_parser_for>>. `parser_for<T>` is an instantiation of
<<ref_basic_parser>> that parses into an object of type `T`, and is what
<<ref_parse_into>> uses under the hood.

Direct serialization doesn't require any special components and works with the
regular <<ref_serializer>> and <<ref_serialize>>.