Obtain a polymorphic wrapper with the specified property.

template<
    typename Property>
any_completion_executor prefer(
    const Property & p,
    typename constraint< traits::prefer_member< const base_type &, const Property & >::is_valid >::type  = 0) const;

Do not call this function directly. It is intended for use with the prefer customisation point.

For example:

any_completion_executor ex = ...;
auto ex2 = asio::prefer(ex, execution::relationship.fork);