Work in progres, please take a look and give early feedback if this is the way we want to structure…

lib/io/system_macos.dart

 // Copyright (c) 2014, the Fletch project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
 part of system;
 
 const int EVFILT_READ   = -1;
 const int EVFILT_WRITE  = -2;
 
 const int EV_ADD      = 0x1;
 const int EV_DELETE   = 0x2;
 const int EV_ENABLE   = 0x4;
 const int EV_DISABLE  = 0x8;
 const int EV_ONESHOT  = 0x10;
 const int EV_CLEAR    = 0x20;
 const int EV_EOF      = 0x8000;
 
 class MacOSAddrInfo extends AddrInfo {
   MacOSAddrInfo() : super._();
   MacOSAddrInfo.fromAddress(int address) : super._fromAddress(address);
 
   get ai_canonname {
     int offset = _addrlenOffset + wordSize;
     return getWord(offset);
   }
 
-  Foreign get ai_addr {
+  ForeignMemory get ai_addr {
     int offset = _addrlenOffset + wordSize * 2;
-    return new Foreign.fromAddress(getWord(offset), ai_addrlen);
+    return new ForeignMemory.fromAddress(getWord(offset), ai_addrlen);
   }
 
   AddrInfo get ai_next {
     int offset = _addrlenOffset + wordSize * 3;
     return new MacOSAddrInfo.fromAddress(getWord(offset));
   }
 }
 
 class KEvent extends Struct {
   KEvent() : super.finalize(6);
@@ skipping 19 matching lines @@
 
   get fflags => getInt32(wordSize + 4);
   get data => getWord(wordSize + 8);
   get udata => getWord(wordSize + 8 + wordSize);
   void set udata(int value) {
     setWord(wordSize + 8 + wordSize, value);
   }
 }
 
 class MacOSSystem extends PosixSystem {
-  static final Foreign _kevent = Foreign.lookup("kevent");
-  static final Foreign _lseekMac = Foreign.lookup("lseek");
-  static final Foreign _openMac = Foreign.lookup("open");
+  static final ForeignFunction _kevent =
+      ForeignLibrary.standard.lookup("kevent");
+  static final ForeignFunction _lseekMac =
+      ForeignLibrary.standard.lookup("lseek");
+  static final ForeignFunction _openMac =
+      ForeignLibrary.standard.lookup("open");
 
   final KEvent _kEvent = new KEvent();
 
   int get FIONREAD => 0x4004667f;
 
   int get SOL_SOCKET => 0xffff;
 
   int get SO_REUSEADDR => 0x4;
 
-  Foreign get _lseek => _lseekMac;
-  Foreign get _open => _openMac;
+  ForeignFunction get _lseek => _lseekMac;
+  ForeignFunction get _open => _openMac;
 
   int _setEvents(bool read, bool write) {
     int eh = System.eventHandler;
     int status = 0;
     if (read) {
       _kEvent.filter = EVFILT_READ;
       status = _retry(() => _kevent.icall$6(eh,
                                             _kEvent,
                                             1,
                                             Foreign.NULL,
@@ skipping 21 matching lines @@
       throw "Listening for both READ_EVENT and WRITE_EVENT is currently"
             " unsupported on mac os.";
     }
     _kEvent.clear();
     _kEvent.ident = fd;
     _kEvent.flags = EV_ADD | EV_ONESHOT;
     _kEvent.udata = System._incrementPortRef(port);
     return _setEvents((mask & READ_EVENT) != 0, (mask & WRITE_EVENT) != 0);
   }
 }