std.socket is missing the following import:

import core.sys.posix.sys.un;

Even when adding in the missing import, the implementation of UnixAddress is broken.

Here's my quick fix for Linux (there may be problems with it), there also needs to be versions for OSX and FreeBSD because sockaddr_un is slightly different.

import std.c.linux.socket;
import core.sys.posix.sys.un;

class UnixAddress: Address
{
	private:
		sockaddr_un sun;

		this()
		{
		}

	public:
	
	    override @property sockaddr* name()
		{
			return cast(sockaddr*)&sun;
		}

		override @property const(sockaddr)* name() const
		{
			return cast(const(sockaddr)*)&sun;
		}

		override @property socklen_t nameLen() const
		{
			return cast(socklen_t) sun.sizeof;
		}

        this(in char[] path)
        {
            sun.sun_family = AF_UNIX;
            sun.sun_path.ptr[0..path.length] = cast(byte[])path;
            sun.sun_path.ptr[path.length] = 0;
        }

        @property string path() const
        {
            return to!string(sun.sun_path.ptr);
        }

        override string toString() const
        {
            return path;
        }
}