Availability.h-like宏 [英] Availability.h -like macro

问题描述

可以使用自定义可用性宏，例如__OSX_AVAILABLE_STARTING。我需要它以相同的方式执行，我只需要更改其名称和版本和参数的数量？

解决方案

是的，当然。 Objective-C是C的一个严格的超集，所以C宏是非常在你的处置，并且该设施只是一组C宏，最终扩展为
gcc的 __ attribute __ 关键字声明函数的特殊属性。 p>

相关声明全部在

• Availability.h


• AvailabilityInternal.h

要刷新，您可以使用 __ OSX_AVAILABLE_STARTING 宏将函数声明标记为支持

  extern void mymacfunc（）__OSX_AVAILABLE_STARTING（__ MAC_10_5，__ IPHONE_NA）; 
  

那么我们需要什么来实现呢？如果你删除他们的
支持两个不同的操作系统（mac，iphone），可用性设施归结为：

1. 一个包含 __ MY_AVAILABLE_STARTING（< version>）的版本参数的宏：

     #define __MY_AVAILABLE_STARTING（_myversion）__MY_AVAILABILITY_INTERNAL ## _ myversion 
     




2. ，像 Availability.h 中那些是上述的有效参数的那些：

     #define __MYVER_2_0 20000 
    #define __MYVER_2_1 20100 
    #define __MYVER_2_2 20200 
    #define __MYVER_3_0 30000 
     




3. 另一组宏，如 AvailabilityInternal.h 中的指定每个版本应该发生什么，不可用，弱等）。同样，这是编译器的函数，请参见 gcc docs （还有很多其他有趣的选项）：

     #define __MY_AVAILABILITY_INTERNAL__MYVER_2_0 __AVAILABILITY_INTERNAL_UNAVAILABLE 
    #define __MY_AVAILABILITY_INTERNAL__MYVER_2_1 __AVAILABILITY_INTERNAL_WEAK_IMPORT 
    #define __MY_AVAILABILITY_INTERNAL__MYVER_2_1 __AVAILABILITY_INTERNAL_REGULAR 
     




4. ，其中buck结束，宏扩展到 __属性__ 设施。

   
   
   

   对于上面的那些，你可以继续使用苹果的宏：

     #define __AVAILABILITY_INTERNAL_DEPRECATED __attribute __（（弃用，可见性（默认）））
    #define __AVAILABILITY_INTERNAL_UNAVAILABLE __attribute __（（不可用，可见性（默认）））
    #define __AVAILABILITY_INTERNAL_WEAK_IMPORT __attribute __ weak_import，visibility（default）））
    #define __AVAILABILITY_INTERNAL_REGULAR __attribute __（（visibility（default）））
     

   或者，当然，你可以定义自己的疯狂。

东西，经常被忽视。祝你好运！

Is it possible to have a custom availability macro like the __OSX_AVAILABLE_STARTING for instance. I need it to perform in the same way, I just need to change its name and the versions and number of parameters?

解决方案

Yes, certainly. Objective-C is a strict superset of C, so C macros are very much at your disposal, and that facility is simply a set of C macros that eventually expand to gcc's __attribute__ keyword to declare special attributes of a function.

The relevant declarations are all in

• Availability.h
• AvailabilityInternal.h

To refresh, you use the __OSX_AVAILABLE_STARTING macro to tag a function declaration as being supported for a particular version, like this:

extern void mymacfunc() __OSX_AVAILABLE_STARTING(__MAC_10_5,__IPHONE_NA);

So what do we need to implement this ourselves? If you strip their support for two different OS (mac, iphone), the availability facility boils down to:

1. A macro that takes a version argument like __MY_AVAILABLE_STARTING(<version>):

   #define __MY_AVAILABLE_STARTING(_myversion) __MY_AVAILABILITY_INTERNAL##_myversion
   

2. Set of version arguments, like those in Availability.h, that are valid arguments for the above:

   #define __MYVER_2_0     20000  
   #define __MYVER_2_1     20100  
   #define __MYVER_2_2     20200  
   #define __MYVER_3_0     30000  
   

3. Another set of macros, like thos in AvailabilityInternal.h that specifies what should happen for each version (regular support, deprecated, unavailable, weak, etc). Again, this is a function of the compiler, see gcc docs (there are lots of other interesting options):

   #define __MY_AVAILABILITY_INTERNAL__MYVER_2_0 __AVAILABILITY_INTERNAL_UNAVAILABLE
   #define __MY_AVAILABILITY_INTERNAL__MYVER_2_1 __AVAILABILITY_INTERNAL_WEAK_IMPORT
   #define __MY_AVAILABILITY_INTERNAL__MYVER_2_1 __AVAILABILITY_INTERNAL_REGULAR
   

4. And finally, where the buck ends, the macros that expand to the __attribute__ facility.

   For the ones I have above, you can just keep using Apple's macros:

   #define __AVAILABILITY_INTERNAL_DEPRECATED         __attribute__((deprecated,visibility("default")))
   #define __AVAILABILITY_INTERNAL_UNAVAILABLE        __attribute__((unavailable,visibility("default")))
   #define __AVAILABILITY_INTERNAL_WEAK_IMPORT        __attribute__((weak_import,visibility("default")))
   #define __AVAILABILITY_INTERNAL_REGULAR            __attribute__((visibility("default")))
   

   Or, of course, you can define your own craziness.

C Macros are powerful stuff, often overlooked. Good luck!

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