...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Set the true branch of the conditional.
template< typename T> deferred_conditional< T, OnFalse > then( T on_true, typename constraint< is_deferred< T >::value >::type * = 0, typename constraint< is_same< typename conditional< true, OnTrue, T >::type, deferred_noop >::value >::type * = 0);