Very useful macro to get around some mutable/immutable assignment issues for basic Foundation types.

FoundationMutabilityType.m

#import <Foundation/Foundation.h>

@interface NSString (FoundationMutabilityType)

- (NSString *)copy;
- (NSMutableString *)mutableCopy;

@end
  
@interface NSDictionary<KeyType, ObjectType> (FoundationMutabilityType)

- (NSDictionary<KeyType, ObjectType> *)copy;
- (NSMutableDictionary<KeyType, ObjectType> *)mutableCopy;

@end

@interface NSArray<ObjectType> (FoundationMutabilityType)

- (NSArray<ObjectType> *)copy;
- (NSMutableArray<ObjectType> *)mutableCopy;

@end

@interface NSSet<ObjectType> (FoundationMutabilityType)

- (NSSet<ObjectType> *)copy;
- (NSMutableSet<ObjectType> *)mutableCopy;

@end

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wincomplete-implementation"
@implementation NSString (FoundationMutabilityType) @end
@implementation NSArray (FoundationMutabilityType) @end
@implementation NSDictionary (FoundationMutabilityType) @end
@implementation NSSet (FoundationMutabilityType) @end
#pragma clang diagnostic pop