Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of Boost. Click here to view this page for the latest version.
PrevUpHomeNext

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

// In header: <boost/log/attributes/value_extraction_fwd.hpp>

template<typename T, typename DefaultT, typename TagT> 
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.


PrevUpHomeNext