copy

Person.h

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN
@interface Person : NSObject

@property (copy, readonly) NSString *firstName;
@property (copy, readonly) NSString *lastName;

-(instancetype)initWithFirstName:(NSString *)firstName lastName:(NSString *)lastName NS_DESIGNATED_INITIALIZER;

@end
NS_ASSUME_NONNULL_END

Person.m

#import "Person.h"

@interface Person ()
@property (copy, readwrite) NSString *firstName;
@property (copy, readwrite) NSString *lastName;
@end

@implementation Person

-(instancetype)initWithFirstName:(NSString *)firstName lastName:(NSString *)lastName {
    if (self = [super init]) {
        self.firstName = firstName;
        self.lastName = lastName;
    }
    return self;
}

@end