SKValueObject

SKValueObject.h

//
//  SKValueObject.h
//  TinyType
//
//  Created by Soroush Khanlou on 5/15/14.
//  Copyright (c) 2014 Soroush Khanlou. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface SKValueObject : NSObject <NSCopying>

- (instancetype)initWithBackingObject:(id)backingObject;

@property (nonatomic, readonly) id backingObject;


@end

SKValueObject.m

//
//  SKValueObject.m
//  TinyType
//
//  Created by Soroush Khanlou on 5/15/14.
//  Copyright (c) 2014 Soroush Khanlou. All rights reserved.
//

#import "SKValueObject.h"

@interface SKValueObject ()

@property (nonatomic, strong) id backingObject;


@end

@implementation SKValueObject

- (instancetype)initWithBackingObject:(id)backingObject {
    self = [super init];
    if (!self) return nil;
    
    _backingObject = backingObject;
    
    return self;
}

- (BOOL)isEqual:(id)other {
    if (other == self) return YES;
    if (![other isKindOfClass:self.class]) return NO;
    return [self isEqualToValueObject:other];
}

- (BOOL)isEqualToValueObject:(SKValueObject*)otherValueObject {
    return [self.backingObject isEqual:otherValueObject.backingObject];
}

- (NSString *)description {
    return [NSString stringWithFormat:@"<%p: %@> {Value: %@}", self, self.class, self.backingObject];
}

- (NSComparisonResult)compare:(SKValueObject*)otherValueObject {
    return [self.backingObject compare:otherValueObject.backingObject];
}

- (NSUInteger)hash {
    return [self.backingObject hash];
}

- (id)copyWithZone:(NSZone *)zone {
    return [[self.class allocWithZone:zone] initWithBackingObject:self.backingObject];
}

@end

Hi! Fan of the blog. One thing I wanted to note was that this implementation does have a possible issue if initialized with a backingObject that has a mutable subclass. The standard example being where you pass in an NSMutableString instance to the initializer -- Since NSCopying isn't enforced on that parameter, we can't copy it on initialization, and therefore it could mutate without the value object wrapper being aware.