Struct template extract_or_default
boost::log::result_of::extract_or_default — A metafunction that allows to acquire the result of the value extraction.
Synopsis
template<typename T, typename DefaultT = T, typename TagT = void>
struct extract_or_default {
};
Description
The metafunction results in a type that is in form of T const&, if T is not an MPL type sequence and DefaultT is the same as T, or value_ref< TypesT, TagT > otherwise, with TypesT being a type sequence comprising the types from sequence T and DefaultT, if it is not present in T already.