最近在研究RunLoop运行机制，想看看他的底层代码是什么样子的，于是百度看看大家如何操作的。最终绝望的发现基本的操作都一样，然并卵。
zhangquaniMac:3456 zq$ cd /Users/zq/Desktop/3456/3456
zhangquaniMac:3456 zq$ clang -x objective-c -rewrite-objc -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk ViewController.m显示异常如下：
clang: warning: using sysroot for 'iPhoneSimulator' but targeting 'MacOSX' [-Wincompatible-sysroot]
warning: include path for stdlibc++ headers not found; pass '-std=libc++' on the
command line to use the libc++ standard library instead
[-Wstdlibcxx-not-found]
1 warning generated.
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:12856:188: warning:
'kCFCalendarUnitWeek' is deprecated: first deprecated in macOS 10.10 - Use
kCFCalendarUnitWeekOfYear or kCFCalendarUnitWeekOfMonth instead
[-Wdeprecated-declarations]
...or NSCalendarUnitWeekOfYear, depending on which you mean"))) = kCFCalend...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:5156:2: note:
'kCFCalendarUnitWeek' has been explicitly marked deprecated here
kCFCalendarUnitWeek __attribute__((availability(macos,introduced=10.4,d...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:22487:16: warning:
'ns_returns_retained' attribute only applies to functions that return an
Objective-C object [-Wignored-attributes]
__attribute__((__ns_returns_retained__)) _Nullable sec_trust_t
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:22493:16: warning:
'ns_returns_retained' attribute only applies to functions that return an
Objective-C object [-Wignored-attributes]
__attribute__((__ns_returns_retained__)) _Nullable sec_identity_t
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:22496:16: warning:
'ns_returns_retained' attribute only applies to functions that return an
Objective-C object [-Wignored-attributes]
__attribute__((__ns_returns_retained__)) _Nullable sec_identity_t
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:22505:16: warning:
'ns_returns_retained' attribute only applies to functions that return an
Objective-C object [-Wignored-attributes]
__attribute__((__ns_returns_retained__)) _Nullable sec_certificate_t
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:22521:16: warning:
'ns_returns_retained' attribute only applies to functions that return an
Objective-C object [-Wignored-attributes]
__attribute__((__ns_returns_retained__)) _Nullable dispatch_data_t
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:22555:16: warning:
'ns_returns_retained' attribute only applies to functions that return an
Objective-C object [-Wignored-attributes]
__attribute__((__ns_returns_retained__)) _Nullable dispatch_data_t
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:22559:16: warning:
'ns_returns_retained' attribute only applies to functions that return an
Objective-C object [-Wignored-attributes]
__attribute__((__ns_returns_retained__)) _Nullable dispatch_data_t
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:50310:13: warning:
'CADisplayLink' is only available on macOS 10.14 or newer
[-Wunguarded-availability-new]
- (nullable CADisplayLink *)displayLinkWithTarget:(id)target selector:(S...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:33690:12: note:
'CADisplayLink' has been explicitly marked partial here
@interface CADisplayLink : NSObject
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:50310:1: note:
annotate 'displayLinkWithTarget:selector:' with an availability attribute
to silence this warning
- (nullable CADisplayLink *)displayLinkWithTarget:(id)target selector:(S...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:52754:18: error:
'UIWebView' is unavailable: not available on macOS
- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRe...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:52702:281: note:
'UIWebView' has been explicitly marked unavailable here
...__attribute__((availability(macos,unavailable))) @interface UIWebView : ...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:52755:30: error:
'UIWebView' is unavailable: not available on macOS
- (void)webViewDidStartLoad:(UIWebView *)webView __attribute__((availabi...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:52702:281: note:
'UIWebView' has been explicitly marked unavailable here
...__attribute__((availability(macos,unavailable))) @interface UIWebView : ...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:52756:31: error:
'UIWebView' is unavailable: not available on macOS
- (void)webViewDidFinishLoad:(UIWebView *)webView __attribute__((availab...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:52702:281: note:
'UIWebView' has been explicitly marked unavailable here
...__attribute__((availability(macos,unavailable))) @interface UIWebView : ...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:52757:18: error:
'UIWebView' is unavailable: not available on macOS
- (void)webView:(UIWebView *)webView didFailLoadWithError:(NSError *)err...
^
/var/folders/qc/wbfmgr1x6f9246c0jt6yqt100000gn/T/ViewController-4ce726.mi:52702:281: note:
'UIWebView' has been explicitly marked unavailable here
...__attribute__((availability(macos,unavailable))) @interface UIWebView : ...
^
9 warnings and 4 errors generated.试了多次，发现还是报同样的错误，于是只能继续耐心的看看还有没有不同的操作，最终得到了一个完美的操作：
zhangquaniMac:~ zq$ cd /Users/zq/Desktop/3456/3456
zhangquaniMac:3456 zq$ xcrun -sdk iphonesimulator clang -rewrite-objc ViewController.m转换成功
补充一下
指定真机
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指定模拟器
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指定SDK版本
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