Why isn't is possible to append a String! via += operator?

Question

As the title says I\'m trying to append text to an implicitly unwrapped optional String via += operator which gives me

\'String!\' is not identical          


        

Answer 1

String! is implicitly unwrapped optional type which is special case of optional type.

As you may know String! is not identical to String. So when you write:

var myOptionalString: String! = "Foo "
myOptionalString += " bar" // error: String! is not identical to 'UInt8'

it will try to find += operator with String! which it could not and the hence error.

if you explicitly unwrap it (you could say then it defies the purpose) works:

 myOptionalString! += " bar"

Answer 2

There's nothing wrong in your code. It looks like in Swift's standard library there's no += operator overload made to work with String optionals.

Taken from the standard library, += is overloaded for String (not for String?)

func +=(inout lhs: String, rhs: String)

Just follow this nice SO answer to view the contents of the Swift standard library to check that

Note

Your code will be better written as:

var myOptionalString: String? = "Foo "
myOptionalString
myOptionalString! += " bar"