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.