Do ivars have to be enclosed in curly braces?

Question

Is it mandatory to enclose instance variables in braces? Or is it just convention?

For example:

#import <Foundation/Foundation.h>    

@interface Person : NSObject
{
    NSString *name;
    int age;
}

Answer 1

Yes, the curly braces are required to declare instance variables. Curly braces right after an @interface or @implementation line mark instance variable declarations. If you omitted the braces, you would simply be declaring global variables.

Answer 2

the curly braces and the enclosed block are used to declare the instance variables of an Objective-C class, and follow a @interface or @implementation declaration.

You can declare variables outside these blocks, but they will use raw C semantics.
For example, Objective-C has instance and class methods, but it doesn't have a clear concept of class variable.
You can still use class variables, with C semantics.

static NSMutableArray *myClassList;

@implementation Person
{
    // this block is actually optional
}

// instance methods
// ...

@end