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Obtain a polymorphic wrapper with the specified property.
template< typename Property> any_io_executor prefer( const Property & p, constraint_t< traits::prefer_member< const base_type &, const Property & >::is_valid > = 0) const;
            Do not call this function directly. It is intended for use with the
            prefer
            customisation point.
          
For example:
any_io_executor ex = ...; auto ex2 = asio::prefer(ex, execution::blocking.possibly);