Resolver service requirements

A resolver service must meet the requirements for an I/O object service, as well as the additional requirements listed below.

In the table below, X denotes a resolver service class for protocol InternetProtocol, a denotes a value of type X, b denotes a value of type X::implementation_type, q denotes a value of type ip::basic_resolver_query<InternetProtocol>, e denotes a value of type ip::basic_endpoint<InternetProtocol>, ec denotes a value of type error_code, and h denotes a value meeting ResolveHandler requirements.

Table 23. ResolverService requirements

expression	return type	assertion/note pre/post-condition
`a.destroy(b);`		From IoObjectService requirements. Implicitly cancels asynchronous resolve operations, as if by calling `a.cancel(b, ec)`.
a.cancel(b, ec);	`error_code`	Causes any outstanding asynchronous resolve operations to complete as soon as possible. Handlers for cancelled operations shall be passed the error code `error::operation_aborted`.
a.resolve(b, q, ec);	ip::basic_resolver_iterator< InternetProtocol>	On success, returns an iterator `i` such that `i != ip::basic_resolver_iterator<InternetProtocol>()`. Otherwise returns `ip::basic_resolver_iterator<InternetProtocol>()`.
a.async_resolve(b, q, h);		Initiates an asynchronous resolve operation that is performed via the `io_service` object `a.get_io_service()` and behaves according to asynchronous operation requirements. If the operation completes successfully, the `ResolveHandler` object `h` shall be invoked with an iterator object `i` such that the condition `i != ip::basic_resolver_iterator<InternetProtocol>()` holds. Otherwise it is invoked with `ip::basic_resolver_iterator<InternetProtocol>()`.
a.resolve(b, e, ec);	ip::basic_resolver_iterator< InternetProtocol>	On success, returns an iterator `i` such that `i != ip::basic_resolver_iterator<InternetProtocol>()`. Otherwise returns `ip::basic_resolver_iterator<InternetProtocol>()`.
a.async_resolve(b, e, h);		Initiates an asynchronous resolve operation that is performed via the `io_service` object `a.get_io_service()` and behaves according to asynchronous operation requirements. If the operation completes successfully, the `ResolveHandler` object `h` shall be invoked with an iterator object `i` such that the condition `i != ip::basic_resolver_iterator<InternetProtocol>()` holds. Otherwise it is invoked with `ip::basic_resolver_iterator<InternetProtocol>()`.