自從apple的obj-c進入2.0后，出現(xiàn)了相對于Legacy模式的Modern模式；Modern模式中出現(xiàn)了一些高級功能(比如ARC)，并且出現(xiàn)了一些新的字面語法，新舊模式的差別可以參考apple官方的：
two Platforms 參考文檔

在linux中（以下均以ubuntu 15.04為例），默認的clang以及gnustep是不支持Modern模式的；需要清楚的是Modern必須由libobjc2以及l(fā)ibgnustep-base.so同時支持才可以實現(xiàn)。
所以我們必須在系統(tǒng)安裝libobjc2和對應的libgnustep-base.so。

確保系統(tǒng)處于“全新”狀態(tài)，所謂的“全新”是指沒有安裝過任何llvm，clang尤其是gnustep的任何文件。如果以前安裝過的化必須全部清除干凈。/usr/local/lib和/usr/lib中不能殘留任何libgnustep*的庫

先密集安裝所需的庫吧（有些是可選項）：

sudo apt-get install cmake sudo apt-get install build-essential git subversion ninja sudo apt-get install libffi-dev libxml2-dev libgnutls-dev libicu-dev sudo apt-get install libblocksruntime-dev libkqueue-dev sudo apt-get install libpthread-workqueue-dev autoconf libtool sudo apt-get install curl sudo apt-get install auto-apt sudo apt-get install libjpeg sudo apt-get install libjpeg-dev libtiff-dev libpng12-dev sudo apt-get install libcups2-dev libfreetype6-dev libcairo2-dev sudo apt-get install libxt-dev libgl1-mesa-dev

然后安裝clang和llvm

下載libobjc2（下載地址）；編譯命令如下:

echo "export CC=clang" >> ~/.bashrc echo "export CXX=clang++" >> ~/.bashrc source ~/.bashrc export CC=clang export CXX=clang++ cd libobjc2 rm -rf build mkdir build cd build cmake .. make debug=no sudo -E make install

實際執(zhí)行中發(fā)現(xiàn)在cmake ..這一步發(fā)生錯誤，錯誤日志如下:

-- The C compiler identification is Clang 3.5.0 -- The CXX compiler identification is Clang 3.5.0 -- Check for working C compiler: /usr/bin/clang -- Check for working C compiler: /usr/bin/clang -- works -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Check for working CXX compiler: /usr/bin/clang++ -- Check for working CXX compiler: /usr/bin/clang++ -- works -- Detecting CXX compiler ABI info -- Detecting CXX compiler ABI info - done -- The ASM compiler identification is Clang -- Found assembler: /usr/bin/clang CMake Error at /usr/share/llvm-3.5/cmake/LLVMConfig.cmake:50 (include):include could not find load file: /usr/lib/llvm-3.5/share/llvm/cmake/LLVMExports.cmake Call Stack (most recent call first):CMakeLists.txt:129 (find_package)CMake Error at /usr/share/llvm-3.5/cmake/LLVMConfig.cmake:53 (include):include could not find load file: /usr/lib/llvm-3.5/share/llvm/cmake/LLVM-Config.cmake Call Stack (most recent call first):CMakeLists.txt:129 (find_package)-- Untested version of LLVM (3.5.0) found. -- Disabling LLVM options unless explicitly enabled. -- No C++ runtime library found -- Looking for include file pthread.h -- Looking for include file pthread.h - found -- Looking for pthread_create -- Looking for pthread_create - not found -- Looking for pthread_create in pthreads -- Looking for pthread_create in pthreads - not found -- Looking for pthread_create in pthread -- Looking for pthread_create in pthread - found -- Found Threads: TRUE -- GNUstep install type set to LOCAL -- Configuring incomplete, errors occurred! See also "/home/wisy/src/libobjc2/build/CMakeFiles/CMakeOutput.log". See also "/home/wisy/src/libobjc2/build/CMakeFiles/CMakeError.log".

不需要到CMakeFiles目錄中去看CMakeError.log，其實出錯原因上面已經(jīng)說的很清楚了，解決辦法卻沒那么簡單，直接做軟鏈接還是會出錯，以下是我的解決辦法：首先下載llvm:

svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm

然后執(zhí)行cmake:

cd llvm mkdir build cd build cmake ..

注意這里后面不需要make，我只要取得cmake生成的一系列*.cmake文件！最終將生成的文件拷貝到指定位置：

cd /usr/lib/llvm-3.5/share/llvm/cmake sudo cp /home/wisy/src/llvm/build/share/llvm/cmake/* .

再次進入libobjc2/build執(zhí)行cmake ..，這回沒有錯誤了。
接下來執(zhí)行安裝libobjc2庫：

make debug=no sudo -E make install

5.下載libdispatch并安裝:

git clone https://github.com/nickhutchinson/libdispatch.git export CC=clang export CXX=clang++ cd libdispatch ./configure make sudo -E make install sudo ldconfig

這時如果用Modern模式編譯objc代碼會出現(xiàn)警告，而且執(zhí)行時也會有警告提示：

clang `gnustep-config --objc-flags` -g0 -O3 -s -fobjc-arc -fobjc-nonfragile-abi -fblocks -lobjc -ldispatch -lgnustep-base -lgnustep-gui `gnustep-config --objc-libs` -o 2 2.mclang: warning: argument unused during compilation: '-shared-libgcc' /usr/bin/ld: warning: libobjc.so.4, needed by /usr/lib/libgnustep-base.so, may conflict with libobjc.so.4.6 /usr/bin/ld: warning: libobjc.so.4, needed by /usr/lib/libgnustep-base.so, may conflict with libobjc.so.4.6 wisy@wisy-X120e:~/src/objc_src$ ./2 Loading two versions of Protocol. The class that will be used is undefined Loading two versions of Object. The class that will be used is undefined 2015-06-11 10:47:20.474 2[21119] (1, hi, 121)

因為libgnustep-base.so還在用老版本的libobjc.so庫，所以需要重新編譯鏈接libgnustep-base.so.

6.下載libgnustep-base；這個在configure后，make出錯，鏈接時報大量的符號找不到定義。后來沒辦法，下載gnustep:

svn co http://svn.gna.org/svn/gnustep/modules/core

然后進入core/scripts目錄，執(zhí)行：

./compile-all

最后在/usr/lib中會出現(xiàn)最新的libgnustep-base.so

如果./compile-all沒有生成.so文件則建議依次到base和gui目錄中去單獨編譯。到這里基本上OK了，可以用以下命令行編譯：

clang `gnustep-config --objc-flags` -g0 -O3 -s -fobjc-arc -fobjc-nonfragile-abi -fblocks -lobjc -ldispatch -lgnustep-base -lgnustep-gui `gnustep-config --objc-libs` -I/usr/include/GNUstep/ -I/usr/local/include/GNUstep/ -o 9 9.m

可以參考老外寫的詳細安裝日志，但我具體實現(xiàn)下來貌似一些步驟無法實現(xiàn)：

https://feloneouscat.wordpress.com/2013/10/25/objective-c-on-ubuntu-12-04-with-blocks-and-arc/

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