Boost C++ Libraries

Convert a value to an object of type T.

Synopsis

Defined in header <boost/json/value_to.hpp>

template<
    class T,
    class Context>
T
value_to(
    value const& jv,
    Context const& ctx);

Description

This function attempts to convert a value to T using

Out of the box the function supports types satisfying SequenceContainer, arrays, arithmetic types, bool, std::tuple, std::pair, std::variant, std::optional, std::monostate, and std::nullopt_t.

Conversion of other types is done by calling an overload of tag_invoke found by argument-dependent lookup. Its signature should be similar to:

template< class FullContext >
T tag_invoke( value_to_tag<T>, const value&, const Context& , const FullContext& );

or

T tag_invoke( value_to_tag<T>, const value&, const Context& );

or

result<T> tag_invoke( value_to_tag<T>, const value& );

The overloads are checked for existence in that order and the first that matches will be selected.

The object returned by the function call is returned by value_to as the result of the conversion.

The ctx argument can be used either as a tag type to provide conversions for third-party types, or to pass extra data to the conversion function.

Constraints

! std::is_reference< T >::value

Exception Safety

Strong guarantee.

Template Parameters

Return Value

jv converted to result<T>.

Parameters

See Also

value_to_tag, value_from, tag_invoke: A general pattern for supporting customisable functions

Convenience header <boost/json.hpp>