Suppressing "'…' is deprecated" when using respondsToSelector

Question

I'm supporting 10.4+ by picking the most-current API at runtime:

if ([fileManager respondsToSelector:@selector(removeItemAtPath:error:)])
    [fileManager removeItemAtPath:downloadDir error:NULL];
else
    [fileManager removeFileAtPath:downloadDir handler:nil];

In this case, 10.5 and up will use removeItemAtPath:error: and 10.4 will use removeFileAtPath:handler:. Great, but I still get compiler warnings for the old methods:

warning: 'removeFileAtPath:handler:' is deprecated [-Wdeprecated-declarations]

Is there a syntax of if([… respondsToSelector:@selector(…)]){ … } else { … } that hints the compiler (Clang) to not warn on that line?

If not, is there a way to tag that line to be ignored for -Wdeprecated-declarations?

---

After seeing some of the answers, let me clarify that confusing the compiler into not knowing what I'm doing is not a valid solution.

Answer 1

I found an example in the Clang Compiler User's Manual that should let me ignore the warning:

if ([fileManager respondsToSelector:@selector(removeItemAtPath:error:)])
    [fileManager removeItemAtPath:downloadDir error:NULL];
else
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
    [fileManager removeFileAtPath:downloadDir handler:nil];
#pragma clang diagnostic pop

It's not ideal, but will work if Clang isn't smart enough to handle this case.

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Edit: …but the version of Clang shipping with Xcode doesn't seem to support it:

warning: pragma diagnostic expected 'error', 'warning', 'ignored', or 'fatal' [-Wunknown-pragmas]

Answer 2

You could declare a separate file that is designated for calling deprecated methods and set the per-file compiler flags in Xcode to ignore -Wdeprecated-declarations. You can then define a dummy function in that file to call the deprecated methods, and thereby avoid the warnings in your real source files.

Answer 3

You can use __MAC_OS_X_VERSION_MIN_REQUIRED (defined in Availability.h) in place of respondsToSelector:

#ifdef __MAC_OS_X_VERSION_MIN_REQUIRED
    // code only compiled when targeting Mac OS X and not iPhone
    // note use of 1050 instead of __MAC_10_5
    #if __MAC_OS_X_VERSION_MIN_REQUIRED < 1050
        // code in here might run on pre-Leopard OS
    #else
        // code here can assume Leopard or later
    #endif
#endif

or:

#ifdef __MAC_10_5
  // code for Leopard or later
#else
  // code for pre-Leopard
#endif

Answer 4

I'm not sure if clang is smart enough to catch this, but if it's not, you could try using performSelector:withObject:withObject: or building and invoking an NSInvocation object.

Answer 5

You could just cast fileManager to an id — ids are able to refer to any Objective-C object, so the compiler isn't supposed to check methods which are called on one:

[(id)fileManager removeItemAtPath:downloadDir error:NULL];

shouldn't raise any warnings or errors.

Of course, this raises other problems — namely, you lose all compile-time checking for methods called on the id. So if you misspell you method name, etc, it wont be caught until that line of code is executed.

Answer 6

If you consider any form of "confusing" the compiler to be an invalid solution, you're probably going to have to live with the warning. (In my book, if you asking how to get rid of a warning, it's unwise to look a gift horse in the mouth and say something is invalid just because it doesn't look like you'd expect.)

The answers that work at runtime involve masking the operation that's happening with dynamic dispatch so the compiler doesn't complain about the deprecated call. If you don't like that approach, you can turn off "Warn About Deprecated Functions" in your Xcode project or target settings, but that's generally a bad idea. You want to know about deprecated APIs, but in this case you want to use it without warning. There are easy and hard ways to do this, and odds are you'd consider all of them "invalid" in some form, but that doesn't prevent them from being effective, even correct. ;-)

One possible way to avoid the warnings yet still select at runtime is to use objc_msgSend() directly:

objc_msgSend(fileManager, @selector(removeFileAtPath:error:), downloadDir, nil];

This is what the Objective-C runtime does under the covers anyway, and should accomplish the result you want with a minimum of fuss. You can even leave the original line commented above it for clarity. I know the documentation says, "The compiler generates calls to the messaging function. You should never call it directly in the code you write." You alone have to decide when it's okay to bend the rules.