https://stackoverflow.com/q/66201708/1271826

InvoiceItem.h

//  InvoiceLine.h

@import Foundation;

NS_ASSUME_NONNULL_BEGIN

@interface InvoiceItem : NSObject

@property (nonatomic, copy, nullable) NSString *title;
@property (nonatomic, copy, nullable) NSString *itemDescription; // because `description` has special meaning in `NSObject`, we’ll call this `itemDescription`
@property (nonatomic, copy, nullable) NSString *cost;
@property (nonatomic, copy, nullable) NSString *tax;

@end

NS_ASSUME_NONNULL_END

And you could use it like so:

InvoiceItem *item = [[InvoiceItem alloc] init];

...

item.title = "foo";

And the .m file is pretty simple, too.

//  InvoiceItem.m

#import "InvoiceItem.h"

@implementation InvoiceItem

- (NSString *)description {
    return [NSString stringWithFormat:@"<InvoiceLine %p; title=%@; itemDescription=%@; cost=%@; tax=%@>", self, self.title, self.itemDescription, self.cost, self.tax];
}

@end

You don't need to implement description, but it makes it so you can easily log it, e.g.

InvoiceItem *item = [[InvoiceItem alloc] init];

...

item.title = "foo";
NSLog(@"%@", item);