Working with 'const' keyword

// Case 1
// A modifiable pointer to a constant NSString.
//
NSString* john = @"John";

NSString* const userName1 = john;

//If we try like below - an error occurs because userName1 is a modifiable pointer to a constant NSString, so its value can't be modified
//userName1 = @"Not John"; // Invalid -> Read-only variable is not assignable

//But lets try to break the pointer itself.

// ARC cannot infer what storage type it should use. So you have to tell it
// This loses the const qualifier, so the compiler is warning you of that fact.
NSString* __strong * notJohn = &userName1;

*notJohn = @"Not John";

NSLog(@"USER 1 name is %@", userName1); //prints Not John

// Case 2
// A constant pointer to an modifiable NSString (its value can't be modified).
//
NSString* tom = @"Tom";

const NSString* userName2 = tom;

tom = @"Not Tom";

userName2 = tom;

NSLog(@"USER 2 name is %@", userName2); // prints TOM 2

// Case 3 - most safe way
// A constant pointer to a constant NSString
//
NSString* bob = @"Bob";

const NSString* const userName3 = bob;

bob = @"Not Bob";

// If we try assigning like below - error occurs
//userName3 = bob; // Bingo we've got error: -> Read-only variable is not assignable