In which situations is it necessary to explicitly use retain and release in automatic memory management (ARC) on iOS platform?

In the iOS environment with ARC (Automatic Reference Counting), developers usually do not manually manage retain and release — the compiler handles this. However, there are rare situations where explicit use of these methods may be necessary:

• Interacting with low-level Objective-C APIs, where ARC cannot correctly determine the lifetime of an object, for example, when using Core Foundation objects that do not support ARC directly. In such cases, manual memory management with CFBridgingRetain and CFBridgingRelease is required.

• When writing Objective-C code using __bridge_retained and __bridge_transfer for conversions between ARC types and Core Foundation.

• In rare cases, when implementing custom classes with non-standard memory management or when avoiding strong reference cycles (retain cycles), although weak and unowned are usually used for this.

Overall, in modern ARC-enabled applications, manual use of retain and release is almost unnecessary and even prohibited by the compiler. If such needs arise, it is advisable to reconsider the architecture or use special bridges for Core Foundation.

Example of usage with Core Foundation:

CFStringRef cfStr = CFStringCreateWithCString(NULL, "Hello", kCFStringEncodingUTF8);
NSString *nsStr = (__bridge_transfer NSString *)cfStr; // ARC takes over management
// Without __bridge_transfer, CFRelease(cfStr) would need to be called manually;