In ObjC, how does one determine whether the object can be changed or not?

In ObjC, how does one determine whether the object can be changed or not?

How to judge whether the object is changeable or not in ObjC?

How can we determine NSString and NSMutableString?

Question

    BOOL result = [@"123" isKindOfClass:[NSMutableString class]];    // A:YES     B:NO

This is simple, of course, B. The String constant is NSString. So the correct answer is A, is there A way to catch up with questions. We recommend that you have an interview with this question.

First, we should use Baidu objc's cluster-like concept and then the factory model. This note only describes how to judge, and opens a portal to fight for monsters.

 

View the results obtained from the console

    id str0 = [NSString alloc];//NSPlaceholderString->NSString    id str1 = [[NSString alloc] init];//__NSCFConstantString->__NSCFString->NSMutableString->NSString    id str3 = [NSString stringWithFormat:@"123"];//NSTaggedPointerString->NSString    id str4 = [NSMutableString alloc];//NSPlaceholderMutableString->NSMutableString->NSString    id str5 = [NSMutableString new];//__NSCFString->NSMutableString->NSString

The String constant, that is, the type obtained by the str1 creation method is _ NSCFConstantString, and the class of NSMutableString is explicit. In any case, be brave enough to question Apple's designs. In addition, the Array and Dictionary at the end do not have such brains. We don't know how many sub-classes are in the black box. According to the inverted big method:

So now you can determine whether a string is variable.

BOOL isMutable = [str isMemberOfClass: NSClassFromString (@ "_ NSCFString")]; // please note that isMemberOfClass: This method should not be used as isKindOfClass:

 

Let's take a look at the console results of Array.

    NSArray* arr0 = 　　　　　　 [[NSArray alloc] init];//__NSArray0->NSArray    NSArray* arr1 = 　　　　　　 [NSArray arrayWithObject:@"123"];//__NSArrayI->NSArray    NSMutableArray* arr3 = 　　[[NSMutableArray alloc] init];//__NSArrayM->NSMutableArray->NSArray

We can find that although NSArray has a large number of sub-accounts, there will be no close kinship like String.

It can be used to determine whether the Array is immutable. You do not need to write the string type.

BOOL notMutable = [arr isKindOfClass:[NSArray class]]&&![arr isKindOfClass:[NSMutableArray class]];

Dictionary is the same as NSArray.

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