Giovanni P. Deretta <gpderetta@gmail.com> wrote:
Pedro Lamarão wrote:
Peter Petrov escreveu:
Why is "resolver" in the "ip::tcp" namespace? A DNS resolver certainly has nothing to do with the TCP protocol. It should be in the "ip" namespace instead.
It shouldn't be in the "ip" namespace either.
The name translation service in any modern operating system can return address objects for any network families it supports.
In practice, getaddrinfo can return addresses for IPv4 and IPv6. There is no reason why it can't return addresses for any other kind of network (unless naming objects in that network is radically different from "host"/"service").
Just because the system resolver (getaddrinfo) could in principle resolve all kind of addresses, it doesn't mean that the asio resolver should.
The asio resolver returns a protocol specific address (actually an iterator to a list of protocol specific addresses) and thus is strongly typed. If the resolver where to be generic, it would return an iterator to an heterogeneous list of addresses: the address (and socket types initialized from the address) would need to be dynamically typed. The asio interface is designed with static (not dynamic) polymorphisms in mind, so the resolver should be protocol specific.
What Giovanni said. After all, it was his suggestion in the review to add this strong typing :) I do feel that the new asio interface strikes the right balance between strong typing (to allow the compiler to detect more errors) and dynamic typing (in that you can use ip::tcp::socket without needing to know if it's IPv4 or IPv6). Note that it is possible to implement a generic socket using asio. You would have to create a runtime-polymorphic protocol class, and then instantiate the basic_*_socket<> and basic_resolver<> templates on it. Cheers, Chris