Basically a Swift abstraction over getifaddrs; a way to enumerate all the network interfaces on the current host, with their core information such as associated addresses & netmasks.
This is intentionally very lightweight, and designed to be very efficient even for cases where you're looking for a small subset of interfaces. e.g. to find all active IPv4 addresses (excluding loopback networks):
try NetworkInterface.all
.filter { $0.up // Only active network interfaces…
&& !$0.loopback } // Ignoring loopback interfaces…
.compactMap(\.address) // That have addresses and…
.filter(\.isIPv4) // Use IPv4.