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A customisation point that attempts to apply a property to an object.
constexpr unspecified prefer = unspecified;
        The name prefer denotes a customisation point object. The expression
        boost::asio::prefer(E, P0, Pn...) for some subexpressions E
        and P0, and where Pn... represents N
        subexpressions (where N is 0 or more, and with types T
        = decay_t<decltype(E)> and Prop0 = decay_t<decltype(P0)>)
        is expression-equivalent to:
      
is_applicable_property_v<T, Prop0> && Prop0::is_preferable
            is not a well-formed constant expression with value true,
            boost::asio::prefer(E, P0, Pn...) is ill-formed.
          E if N == 0 and the expression
            Prop0::template static_query_v<T> == Prop0::value()
            is a well-formed constant expression with value true.
          (E).require(P0) if N == 0 and the
            expression (E).require(P0) is a valid expression.
          require(E, P0) if N == 0 and the
            expression require(E, P0) is a valid expression with overload
            resolution performed in a context that does not include the declaration
            of the require customization point object.
          (E).prefer(P0) if N == 0 and the
            expression (E).prefer(P0) is a valid expression.
          prefer(E, P0) if N == 0 and the
            expression prefer(E, P0) is a valid expression with overload
            resolution performed in a context that does not include the declaration
            of the prefer customization point object.
          E if N == 0.
          boost::asio::prefer(boost::asio::prefer(E, P0), Pn...)
            if N > 0 and the expression boost::asio::prefer(boost::asio::prefer(E,
            P0), Pn...) is a valid expression.
          boost::asio::prefer(E, P0, Pn...) is ill-formed.
          
        Header: boost/asio/prefer.hpp
      
        Convenience header: boost/asio.hpp