Construct the adapted executor from the inner executor type.

template<
    typename InnerExecutor1>
executor_with_default(
    const InnerExecutor1 & ex,
    constraint_t< conditional_t< !is_same< InnerExecutor1, executor_with_default >::value, is_convertible< InnerExecutor1, InnerExecutor >, false_type >::value >  = 0);