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  • Feature Name: ipaddr-common-methods
  • Start Date: 2016-07-06
  • RFC PR: (leave this empty)
  • Rust Issue: (leave this empty)


net::Ipv4Addr and net::Ipv6Addr both expose methods like is_loopback() and is_multicast(). net::IpAddr should expose those directly rather than requiring a redundant match.


If I have an IpAddr and I want to test whether or not it is a loopback address, I do not need or want to know if it is v4 or v6. As of Rust v1.7.0, testing if an IpAddr addr is a loopback address looks like this:

match addr {
    IpAddr::V4(v4addr) => v4addr.is_loopback(),
    IpAddr::V6(v6addr) => v6addr.is_loopback(),

If this RFC is adopted, this would become simply


which is much simpler.

Additionally, net::SocketAddr.ip() and .port() do the same thing elsewhere in the standard library.

Detailed design

Since several methods, like is_loopback() and is_multicast(), exist in both net::Ipv4Addr and net::Ipv6Addr, it seems natural to add those methods to net::IpAddr.

These implementations would be written as matches like the one given above, similarly to the implementation of net::SocketAddr.ip(), which is a method that seems to exist for the same reason.

The method signatures should be as follows:

impl IpAddr {
    fn is_unspecified(&self) -> bool { ... }
    fn is_loopback(&self) -> bool { ... }
    fn is_global(&self) -> bool { ... }
    fn is_multicast(&self) -> bool { ... }
    fn is_documentation(&self) -> bool { ... }


This makes the standard library slightly larger and increases overhead in changes to Ipv4Addr and Ipv6Addr (since new methods in both structs would be added to IpAddr as well).


This RFC does not make anything new possible. It simply makes something slightly easier. As such, to simply leave things as they are would be the primary alternative.

Unresolved questions

Are Ipv4Addr.is_link_local() and Ipv6Addr.is_unicast_link_local() the same? If so, which name should be used in IpAddr?