Objective C switch statements and named integer constants

Question

I have a controller which serves as a delegate to two scrollviews which are placed in view managed by aforementioned view controller.

To distinguish between two scroll views I'm trying to use switch statement (instead of simple pointer comparison with if statement). I have tagged both scroll views as 0 and 1 like this

NSUInteger const kFirstScrollView = 0;
NSUInteger const kSecondScrollView = 1;

When I try to use these constants in a switch statement, the compiler says that case statements are not constants.

switch (scrollView.tag) {
    case kFirstScrollView: {
      // do stuff
    }
    case kSecondScrollView: {
      // do stuff
    }
}

What am I doing wrong?

Make your constants static too; compiler issue I'm sure, but that seems to fix. For some reason compiler doesn't think that just `const` is really constant, but `const static` is. I'm sure there is some weird abstract reason in the docs somewhere — Albert Renshaw, Jun 29 '18 at 18:26

score 16 · Accepted Answer · answered Dec 20 '10 at 08:41

16

This can be solved through the use of an anonymous (though not necessarily so) enum type:

enum {
    kFirstScrollView = 0,
    kSecondScrollView = 1
};

switch (scrollView.tag) {
    case kFirstScrollView: {
      // do stuff
    }
    case kSecondScrollView: {
      // do stuff
    }
}

This will compile without errors.

answered Dec 20 '10 at 08:41

Aidan Steele

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This is a workable solution and is what I use, but I don't understand why the constants aren't working. – Matthew Frederick Dec 20 '10 at 08:47

score 8 · Answer 2 · edited May 23 '17 at 12:08

8

This is because case statement requires constant expression. Now in C and thus in Obj-C making a variable const does not create a true constant. Thus you are getting this error. But if you use C++ or Obj-C++ then this will work.

Some more hint is available here and here.

edited May 23 '17 at 12:08

Community

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1

answered Dec 20 '10 at 08:50

taskinoor

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So, how can we create constants in Objective-C then? #define MY_CONSTANT 123 would be one way but Is that the only one? – nacho4d Dec 20 '10 at 08:58
2

define and enum. Thay both create true constant in C/Obj-C. – taskinoor Dec 20 '10 at 09:07

Objective C switch statements and named integer constants

2 Answers2

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