Why Xcode 12.5 errs when using Class as a key in NSDictionary?

Question

Created Feb ’21

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I downloaded Xcode 12.5 Beta and now an existing project does not compile with errors telling I can't use Class as a key in NSDictionary.

Code Block Cannot initialize a parameter of type 'id<NSCopying>  _Nonnull const __unsafe_unretained' with an rvalue of type 'Class'

I have assumes so far that while Class does not conform to NSCopying, it is safe to use as a dictionary key because it implements copy and copyWithZone:.

Did anything change with that regard in the compiler/runtime shipped with Xcode 12.5? Is it safe (and endorsed practice) to cast to id<NSCopying> to silence these errors?

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Answer 1

jayxiang OP

Apr ’21

1

0

Answer 2

DTS Engineer OP

Apple

Apr ’21

Can you post a snippet of code that triggers this issue?

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0

Answer 3

dsmo OP

Apr ’21

Code Block NSArray<id<FBObjectReference>> *FBGetObjectStrongReferences(id obj,
                              NSMutableDictionary<Class, NSArray<id<FBObjectReference>> *> *layoutCache) {
 NSMutableArray<id<FBObjectReference>> *array = [NSMutableArray new];
 __unsafe_unretained Class previousClass = nil;
 __unsafe_unretained Class currentClass = object_getClass(obj);
 while (previousClass != currentClass) {
  NSArray<id<FBObjectReference>> *ivars;
   
  if (layoutCache && currentClass) {
   ivars = layoutCache[currentClass];
  }
   
  if (!ivars) {
   ivars = FBGetStrongReferencesForClass(currentClass);
   if (layoutCache && currentClass) {
    layoutCache[currentClass] = ivars;
   }
  }
  [array addObjectsFromArray:ivars];
  previousClass = currentClass;
  currentClass = class_getSuperclass(currentClass);
 }
 return [array copy];
}

Same issue here. This won't compile on Xcode 12.5

0

Answer 4

annomusa OP

Apr ’21

Yes, apparently Xcode 12.5 are using Clang 10 that require you to cast it to id<NSCopying>
Example: https://github.com/facebook/FBRetainCycleDetector/pull/95/files

And if you are using Cocoapods, FBRetainCycleDetector makes that error, you need to specify the commit hash to make sure it using the latest version

Code Block rubypod 'FBRetainCycleDetector', { :git => 'https://github.com/facebook/FBRetainCycleDetector.git', :commit => '32c4afc1' }

0

Answer 5

simcha OP

Apr ’21

Code Block          if ( !animationOperation.isCanceled ) {          if ( !period.startValue ) {
            [period setStartValueFromObject:animationOperation.boundObject propertyGetter:animationOperation.boundGetter];
          }
          Class valueClass = period.valueClass;
          CGFloat progress = timingFunction(currentTime - startTime, duration);
          CPTDictionary *parameters = @{
            CPTAnimationOperationKey: animationOperation,
            CPTAnimationValueKey: [period tweenedValueForProgress:progress],
            CPTAnimationValueClassKey: valueClass ? valueClass : [NSNull null], /* this line won't compile  in xcode 12.5  the error message is: Incompatible operand types ('Class' and 'NSNull * _Nonnull')*/
            CPTAnimationStartedKey: @(started),
            CPTAnimationFinishedKey: @(currentTime >= endTime)
          };
          // Used -performSelectorOnMainThread:... instead of GCD to ensure the animation continues to run in all run loop common modes.
          [self performSelectorOnMainThread:@selector(updateOnMainThreadWithParameters:)
                      withObject:parameters
                    waitUntilDone:NO
                        modes:runModes];
          if ( currentTime >= endTime ) {
            [expiredOperations addObject:animationOperation];
          }
        }

Upgraded today to Xcode 12.5, existing project build failed.
The code snippet source is from CorePlot: https://github.com/core-plot/core-plot/blob/master/framework/Source/CPTAnimation.m line 339

What should i do to avoid from this fail?
(without changing the source code)

Thank you!

1

Answer 6

-NT- OP

May ’21

Has anyone found a solution yet? I really do not want to modify a 3rd party library in order to make my project work.

0