正确将32位方法更新为64位支持

Question

I have a method I am trying to update to 64-bit support for my app. I have lots of these warnings .

The issue is with the below example. I get the warning:

Implicit conversion loses integer precision NSInteger to int

- (int)  aMethod {
    NSUserDefaults *u = [NSUserDefaults standardUserDefaults];
    return [u integerForKey:@"someKey"];
}

If I change the return type to NSInteger I get

Conflicting return type in implementation of aMethod int vs NSInteger aka long

-(NSInteger)  aMethod {
    NSUserDefaults *u = [NSUserDefaults standardUserDefaults];
    return [u integerForKey:@"someKey"];
}

I have tried casting the return type

return (NSInteger)[u integerForKey:@"someKey"];

or

return (long)[u integerForKey:@"someKey"];

But I can't get the error to go away unless I cast it to (int)

return (int)[u integerForKey:@"someKey"];

I have read many SO questions but I can't seem to get a good answer.

What is the proper way of updating this method?

Answer 1

The method:

- (int) aMethod ...

returns a value of type int . The method may first declared, probably in a header ( .h ) file, and then defined in an implementation ( .m ) file.

The statement:

return [u integerForKey:@"someKey"];

returns the result of calling integerForKey: , which is a value of type NSInteger .

NSInteger is not a type defined by the (Objective-)C language , rather it is a type alias ( typedef ) defined in the frameworks intended to represent the "natural" integer size on the platform. It is an alias for int on 32-bit platforms and long on 64-bit.

So your compiler error is telling you that the (now) 64-bit value is being truncated to fit a 32-bit result. There is no single right way to fix this, it depends on what the use of the value associated with @someKey is:

• If the value should now be 64-bit then change the return type of aMethod ; both in its separate declaration, if it has one, and in its implementation; to NSInteger . You will also need to check that wherever the method is called that returning an NSInteger value is acceptable, and you may need to make follow-on changes to variable types etc. You also need to look at places where the value associated with the key is set.
• If the value associated with the key may remain as 32-bit then you can use intForKey: instead of integerForKey and leave the return type as is. You should also change where the key is set to store an int

HTH

Correction

There is (no longer?) a convenience method intForKey: on NSUserDefaults . Alternatives include: integerForKey: and casting; objectForKey: to obtain an NSNumber reference and then intValue ; etc.