Key-Value Coding (KVC) in Cocoa

Key-Value Coding - directly set or get a property of an object by the property name - the key.

#import <Foundation/Foundation.h>

@interface Person : NSObject
{
    NSString* firstName;
    NSString* lastName;
}

@end

@implementation Person

- (id)init
{
    [super init];
    firstName = [[NSString alloc] init];
    lastName = [[NSString alloc] init];
    return self;
}

- (void)dealloc
{
    [firstName release];
    [lastName release];
    [super dealloc];
}

@end

int main() 
{
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    Person* person = [[Person alloc] init];
    
    [person setValue:@"Pavel" forKey:@"firstName"];
    [person setValue:@"Gnatyuk" forKey:@"lastName"];
    
    NSLog(@"Name: %@", [person valueForKey:@"firstName"]);
    NSLog(@"Last Name: %@", [person valueForKey:@"lastName"]);
    
    [person release];
    [pool drain];
    return 0;
}

Mac OS X Reference Library. Key-Value Coding Fundamentals
Cocoa with Love. 5 key-value coding approaches in Cocoa
The Unix Geek. An Introduction to Key-Value Coding in Cocoa.
Thecacao. Key-Value Coding (KVC) and Generic Programming.

I think KVC is the same as the properties in C#. It is easy to understand how it's implemented. For example:
CodeProject. Implementing Properties in C++.

I think the same can be implemented much easier:

#include <iostream>
using namespace std;

class CPerson
{
    char* firstName;
    char* lastName;
    
    void setValue(char*& var, const char* value)
    {
        if (var)
        {
            free(var);
            var = NULL;
        }
        if (value == NULL)
            return;
        var = strdup(value);
    }
    
public:
    CPerson() : firstName(NULL), lastName(NULL) {}
    ~CPerson()
    {
        if (firstName)
            free(firstName);
        if (lastName)
            free(lastName);
    }
    
    const char* get(const char* key)
    {
        if (strcmp(key, "firstName") == 0)
            return firstName;
        if (strcmp(key, "lastName") == 0)
            return lastName;
        return NULL;
    }
    
    void set(const char* key, const char* value)
    {
        if (strcmp(key, "firstName") == 0)
            return setValue(firstName, value);

        if (strcmp(key, "lastName") == 0)
            return setValue(lastName, value);
        return;
    }

};

int main (int argc, char * const argv[]) 
{
    CPerson person;
    person.set("firstName", "Pavel");
    person.set("lastName", "Gnatyuk");
    cout << "Name: " << person.get("firstName") << endl;
    cout << "LastName: " << person.get("lastName") << endl;
    return 0;
}

It is a very simple way. I've never seen NSKeyCodingValue protocol implementation in Cocoa. Of course, it is a really generic and more complicated solution.