Question

In objective-c, is

for (Foo *foo in fooList) ...

more like which of the following

@interface Bar : Foo ...

for (Foo *f in fooList) {
    // A:
    if ([f isMemberOfClass:[Foo class]]) ... // dont include Bar's

    // B:
    if ([f isKindOfClass:[Foo class]]) ... // both Foos and Bars
}

Answer 1

It’s not like either.

The type of foo in the for() part is only a hint to the compiler so it can give out the relevant error messages. At run time, all the objects are just objects and as long as they all implement the methods used in the block, there will be no errors. For example:

NSString* aString = @"20";
[anArray addObject: aString];
for (NSNumber* foo in anArray)
{
    NSLog(@"%d", [foo intValue]);
}

will iterate over all the objects in the array and send intValue to each one no matter what type they are including the NSString at the end. If every object implements intValue it will work just fine (as NSString does). If there is an object in the array that does not implement intValue, an exception will most likely be thrown.