Exit Zen
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Functions like <<ref_value_if_object,`value::if_object`>> actually return a pointer to the object if the value is an object, otherwise they return null. This allows them to be used both in boolean contexts as above, and in assignments or conditional expressions to capture the value of the pointer:
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Description
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However, sometimes shared ownership is needed. Specifically, that the lifetime extension of the memory resource should be automatic. For example, if a library wants to return a container which owns an instance of the library's custom memory resource as shown below:
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of JSON texts each contained in a single contiguous character buffer, returning each result as a <<ref_value>>.
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Parsing
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Parses the input using an instance of
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which rules out the most important type of allocator, a local arena-based implementation.
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To facilitate debugging and ease of output, library container types may be written to standard output streams using the stream operator:
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a| The result is a number equal to input and has the type
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http://www.boost.org/development/tests/master/developer/json.html[image:https://img.shields.io/badge/matrix-master-brightgreen.svg[Matrix]]
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types. |===
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a `std::string` parameter and two `size_type` parameters that specify a
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Combining Contexts
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While overloads of `tag_invoke` called by <<ref_value_to>> take the form:
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Formatted Output
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After a <<ref_value>> is constructed, its kind can change depending on what is assigned to it, or by calling functions such as <<ref_value_emplace_array,`value::emplace_array`>> or <<ref_value_emplace_bool,`value::emplace_bool`>>. If the assignment is successful, in other words it completes without any exceptions then the value is replaced. Otherwise, the value is unchanged. All operations which can fail to modify a value offer the strong exception safety guarantee.
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<<ref_get_null_resource>>
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This can be worked around by declaring the container to use a custom allocator (perhaps using a `std::shared_ptr< std::pmr::memory_resource >` as a data member). This hinders library composition; every library now exports unique, incompatible container types. A raw memory resource pointer is also easy to misuse:
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<<ref_stream_parser>>
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JSON can be parsed into the value container in one step using a free function. In the following snippet, a parse error is indicated by a thrown exception:
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