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A customisation point that queries the value of a property.
constexpr unspecified query = unspecified;
The name query denotes a customization point object. The expression
asio::query(E, P) for some subexpressions E and
P (with types T = decay_t<decltype(E)> and
Prop = decay_t<decltype(P)>) is expression-equivalent
to:
is_applicable_property_v<T, Prop> is not a well-formed
constant expression with value true, asio::query(E,
P) is ill-formed.
Prop::template static_query_v<T> if the
expression Prop::template static_query_v<T> is a well-formed
constant expression.
(E).query(P) if the expression (E).query(P)
is well-formed.
query(E, P) if the expression query(E,
P) is a valid expression with overload resolution performed in
a context that does not include the declaration of the query
customization point object.
asio::query(E, P) is ill-formed.
Header: asio/query.hpp
Convenience header: asio.hpp