Key-Value Coding with custom getter, setter and ivar - objective-c

Question

I'm wondering how Key-Value Coding, to access a property value, works in Objective-C when this property has a custom getter, setter and ivar defined. According to Accessor Search Patterns the runtime will first search for a getter method and fall back to finding an ivar using the reflection string.
According to the search pattern, when neither a getter nor an ivar are found, an exception should be thrown.
However, when I run the following code:
#import <Foundation/Foundation.h>
#interface Class1 : NSObject {
NSInteger prop;
}
#property (getter=customGetter,setter=customSetter:) NSInteger prop;
#end
#implementation Class1
#synthesize prop = customIvar;
#end
int main() {
Class1 *class1;
// Create and give the properties some values with KVC...
class1 = [[Class1 alloc] init];
class1.prop = 9;
NSLog(#"Set value to 9 with direct access");
// Directly access value, should return 9.
NSLog(#"Direct access: %ld", class1.prop);
// Set with setValue:forKey: to 20.
NSLog(#"Set value to 20 with KVC");
[class1 setValue:[NSNumber numberWithInt:20] forKey:#"prop"];
// Directly access value.
NSLog(#"Direct access: %ld", class1.prop);
// Access value using KVC
NSNumber *propVal = [class1 valueForKey:#"prop"];
NSLog(#"ValueForKey access: %d", [propVal intValue]);
}
I get this output:
Set value to 9 with direct access
Direct access: 9
Set value to 20 with KVC
Direct access: 9
ValueForKey access: 20
It seems that I get two different values: values that are set by directly accessing the property are retrieved when reading directly from the property (9). Values that are set using Key-Value Coding are retrieved by using Key-Value Coding (20).
Does anyone know how this works internally? Is this behaviour expected and am I missing something?

Answer 1

Add the following method to your Class1:
- (void) showVars
{
NSLog(#"->prop %ld | ->customIVar %ld", prop1, customIvar);
}
and call it after you alter your property and you will see what is going on.
Read the reference you linked to, what does it say about the search for a getter and setter?
You've found your answer.
Is it well documented? Probably not, Objective-C & Cocoa have no formal semantic description :-(
HTH