Question

is it possible to specify that a NSMutableArray can only contain a certain type of objects.
For example, if I want to store only this kind of objects :

@interface MyObject : NSObject {
    UInt8 value; 
}

In order to be able to use the instance variable like this :

- (void)myMethod:(NSMutableArray *)myArray{
    for (id myObject in myArray){
        [self otherMethod:myObject.value];
    }
}

because I’m getting this error :

request for member 'value' in something not a structure or union

Thank you for your help

Answer 1

You are getting that error, because for as far as Objective-C is concerned, myObject is of the non-type id, which doesn’t support the value property. To make Objective-C aware of the fact it’s always dealing with a MyObject in this loop, you’ll have to tell it the myObject object is an instance of MyObject.

for (MyObject *myObject in myArray) {

Also, you have to make sure the value ivar is accessible using dot-notation by implementing getter and setter methods for it. You can do this yourself by implementing -value and -setValue:, or you can use @property and @synthesize to let Objective-C do this.