Objective-C: custom BOOL access methods (getter & setter)

I know that someone already asked about writing getter and setter for the variable BOOL . But, if I define custom methods getter and setter setImmediateand isImmediate, accordingly, I would like it to passcode.immediate = NOwork as well.

I don't have instance variables, but maybe I need one? I could add one for NSDate *lastUnlocked.

Here's the corresponding code:

// PasscodeLock.h

extern NSString *const kPasscodeLastUnlocked;

@interface PasscodeLock : NSObject {

}

- (BOOL)isImmediate;
- (void)setImmediate:(BOOL)on;

- (NSDate *)lastUnlocked;
- (void)resetLastUnlocked;
- (void)setLastUnlocked:(NSDate *)lastUnlocked;

@end


// PasscodeLock.m

#import "PasscodeLock.h"

NSString *const kPasscodeLastUnlocked    = @"kPasscodeLastUnlocked";

@implementation PasscodeLock

#pragma mark PasscodeLock

- (BOOL)isImmediate {
    return self.lastUnlocked == nil;
}

- (void)setImmediate:(BOOL)on {
    if (on) {
        [self resetLastUnlocked];
    } else {
        self.lastUnlocked = nil;        
    }
}

- (NSDate *)lastUnlocked {
    return [[NSUserDefaults standardUserDefaults] objectForKey:kPasscodeLastUnlocked];
}

- (void)resetLastUnlocked {
    NSDate *now = [[NSDate alloc] init];
    self.lastUnlocked = now;
    [now release];
}

- (void)setLastUnlocked:(NSDate *)lastUnlocked {
    [[NSUserDefaults standardUserDefaults] setObject:lastUnlocked forKey:kPasscodeLastUnlocked];
}

Then in the view controller, which has PasswordLock *passwordLockas an instance variable, I want to do it passcode.immediate = NO, but I get the error "Property" immediate "could not be found on an object like" PasscodeLock *. "

How can I make it passcode.immediate = NOwork?