"= Non-Throwing Conversions For the case where throwing exceptions is undesirable, Boost.JSON also provides a non-throwing version of <<ref_value_to>>, the function template <<ref_try_value_to>>. It returns {ref_result}, a specialised variant that either holds a value or an {ref_error_code}." There\'s no non-throwing equivalent for <<ref_value_from>>. This is simply because we haven\'t yet encountered a situation where <<ref_value_from>> needed to communicate an error to the caller. 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: ``` result_for<T, value>::type tag_invoke( const try_value_to_tag< T >&, const value& ); ``` For the class `ip_address` from the section <<custom_conversions>> this overload may look like this: The overload lets us use `ip_address` with <<ref_try_value_to>>. If <<ref_try_value_to>> is used with a type, for which there\'s no `tag_invoke` overload of the form described in this section, but there is one of the form intended for <<ref_value_to>>, then the library still tries to perform the conversion. It uses the throwing overload, and attempts to convert any thrown exception into an {ref_error_code}. Note, though, that such approach will likely be slower then a dedicated overload. The opposite is also true: if there\'s a `tag_invoke` overload intended for <<ref_try_value_to>>, but not for <<ref_value_to>>, then calling <<ref_value_to>> will invoke the non-throwing overload, then construct a {ref_system_error} from the {ref_error_code} and throw it. Due to these fallbacks, it is recommended that users provide the overload from this section, rather then the other one, if they ever intend to use <<ref_try_value_to>>.