Exit Zen
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The interface and functionality of <<ref_string>> is the same as {std_string} except that:
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In cases where you know that a <<ref_value>> contains a number but don't know its <<ref_kind>>, `value::to_number` can be used to convert the <<ref_value>> to an arithmetic type:
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These `tag_invoke` overloads take an extra `as_string` parameter, which disambiguates this specific representation of `ip_address` from all other potential representations. In order to take advantage of them one needs to pass an `as_string` object to <<ref_value_from>> or <<ref_value_to>> as the last argument:
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Previously a number of conversion type traits, like <<ref_is_tuple_like>> or <<ref_is_sequence_like>>, were introduced. The library tries the traits one after another and uses the implementation that corresponds to the first matching trait. In some cases, though, a type would match a trait with a higher priority, but the user intends for it to belong to a lower priority category. If this happens the user can specialize the trait that's not supposed to match for that type to be an equivalent of `std::false_type`.
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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.
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Iterators are ordinary pointers, and may become invalidated on insertions
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The library provides non-throwing conversions for all the categories of types it supports with <<ref_value_to>>. If a user wants to use it with custom types, an overload of `tag_invoke` of this form needs to be provided:
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After that the definitions of `tag_invoke` overloads should be provided. These overloads have to be templates, since <<ref_value>> is only forward-declared and hence is an incomplete type.
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As the conversion result is set via an output parameter of type `value&`, the intended <<ref_storage_ptr>> is correctly propagated. But users still should take care to not create temporaries using the default {ref_memory_resource} by accident.
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include::../../README.adoc[]
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:leveloffset: +1
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include::parsing.adoc[] include::serializing.adoc[]
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:std_array: pass:q[https://en.cppreference.com/w/cpp/container/array[`std::array`]] :std_initializer_list: pass:q[https://en.cppreference.com/w/cpp/utility/initializer_list[`std::initializer_list`]] :std_complex: pass:q[https://en.cppreference.com/w/cpp/numeric/complex[`std::complex`]] :std_hash: pass:q[https://en.cppreference.com/w/cpp/utility/hash[`std::hash`]] :std_memory_resource: pass:q[https://en.cppreference.com/w/cpp/memory/memory_resource[`std::pmr::memory_resource`]] :std_monostate: pass:q[https://en.cppreference.com/w/cpp/utility/variant/monostate[`std::monostate`]] :std_ostream: pass:q[https://en.cppreference.com/w/cpp/io/basic_ostream[`std::ostream`]] :std_polymorphic_allocator: pass:q[https://en.cppreference.com/w/cpp/memory/polymorphic_allocator[`std::pmr::polymorphic_allocator`]] :std_string: pass:q[https://en.cppreference.com/w/cpp/string/basic_string[`std::string`]] :std_unordered_map: pass:q[https://en.cppreference.com/w/cpp/container/unordered_map[`std::unordered_map`]] :std_uses_allocator: pass:q[https://en.cppreference.com/w/cpp/memory/uses_allocator[`std::uses_allocator`]] :std_vector: pass:q[https://en.cppreference.com/w/cpp/container/vector[`std::vector`]] :std_tuple: pass:q[https://en.cppreference.com/w/cpp/utility/tuple[`std::tuple`]]
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https://github.com/boostorg/json/tree/develop[`develop`]
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The library also allows changing and adding deeply nested elements. The function <<ref_value_set_at_pointer>> traverses the value similarly to <<ref_value_at_pointer>>, but additionally, it can create missing elements in certain cases:
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If the <<ref_value>> does not contain a number, or if the conversion is to an integer type `T` and the number cannot be represented exactly by `T`, the conversion will fail. Otherwise, the result is the number converted to `T` as-if by `static_cast`:
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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.
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and removals.
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As discussed previously, we prefer to define a non-throwing overload of `tag_invoke` for <<ref_try_value_to>>, rather then the throwing overload for <<ref_value_to>>, as the latter can fallback to the former without performance degradation.
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For example, consider this alternative implementation of `tag_invoke` for `ip_address` from the section <<custom_conversions>>.
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