  NS -- the Cocoa interface for macOS and compatible systems
  ----------------------------------------------------------

This directory contains files needed to build Emacs on system based on
NextStep (NS), including macOS and GNUstep, using the Cocoa API.


  HISTORY


The Nextstep (NS) interface of GNU Emacs was originally written in
1994 for NeXTSTEP systems running Emacs 19 and subsequently ported to
OpenStep and then Rhapsody, which became Mac OS X.  In 2004 it was
adapted to GNUstep, a free OpenStep implementation, and in 2008 it was
merged to the GNU Emacs trunk and released with Emacs 23.  Around the
same time a separate Mac-only port using the Carbon APIs and
descending from a 2001 Mac OS 8/9 port of Emacs 21 was removed. (It
remains available externally under the name "mac".)


  OVERVIEW OF COCOA AND OBJECTIVE-C

Cocoa is an API for the Objective-C language, an objective oriented
superset of C.  Anybody with experience with iOS or modern macOS
application development should feel at home.

A method call in Objective-C differs from most other languages in the
fact that it doesn't have a normal name.  Instead, the method name is
made up of the name of each parameter.  An exception to this rule are
methods without parameters.

The following calls a method in the object 'anObject'.

    [anObject alpha:1 beta:2 gamma:3];

Classes are declared like the following:

    @interface AClassName
    {
      // A class method.
      + (TYPE)name1:(TYPE)param1

      // An object method.
      - (TYPE)name1:(TYPE)param1 name2:(TYPE)param2;
    }
    @end


  GUIDELINES

* Adhere the to the FSF philosophy that a feature in GNU software
  should not only be available on non-free systems.

* People with varying Cocoa and Objective-C skills will read and
  modify the NS code over a long period of time.  Keep the code simple
  and avoid language constructs that makes the code hard to maintain.

* Don't use macros and types intended for the XCode Interface Builder,
  like 'IBAction'.

* The NS interface should work on all version of macOS from Mac OS X
  10.6.8 (Snow Leopard) to the latest official release.

* Under macOS, it is possible to build Emacs using NS, X11, or console
  only.  A new macOS feature should work in all appropriate builds.


  TRACING SUPPORT

The NS interface features a printf-based trace package that prints the
call tree of selected functions in the Cocoa interface, plus various
extra information.  It can be enabled by uncommenting the line
defining 'NSTRACE_ENABLED' in "nsterm.h".  To enable more output,
uncomment the lines defining symbols starting with 'NSTRACE_GROUP'.


  GNUSTEP AND OTHER COMPATIBLE SYSTEMS

The NS interface works on systems compatible with macOS, for example
GNUstep.  Even though they are less frequently used, this is important
for a number of reasons:

* It supports the GNUstep project and provides an Emacs with the same
  look-and-feel as the rest of the system.

* This allows other Emacs developers to test their changes on the NS
  interface without having access to a macOS machine.

* If a feature in the NS interface work on free systems like GNUstep,
  this meets the FSF requirement that features in GNU software should
  not only be available on non-free systems.


  SEE ALSO

The src/ns... files contains the C and Objective-C parts.

The lisp/term/ns-win.el file contains the lisp part of the NS
interface.

The INSTALL file in this directory for compilation instructions.

The Nextstep section in the etc/TODO file for a list of ideas for
future development.


----------------------------------------------------------------------
Copyright 2008-2019 Free Software Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
