StaticString

Instances of the StaticString type are immutable.

StaticString provides only low-level access to its contents, unlike Swift’s more commonly used String type. A static string can use either of the following as its storage:

• a pointer to a null-terminated sequence of UTF-8 code units:

  let emoji: StaticString = "\u{1F600}"
  emoji.hasPointerRepresentation  //-> true
  emoji.isASCII                   //-> false
  emoji.unicodeScalar             //-> Fatal error!
  emoji.utf8CodeUnitCount         //-> 4
  emoji.utf8Start[0]              //-> 0xF0
  emoji.utf8Start[1]              //-> 0x9F
  emoji.utf8Start[2]              //-> 0x98
  emoji.utf8Start[3]              //-> 0x80
  emoji.utf8Start[4]              //-> 0x00

• a single Unicode scalar value, under very limited circumstances:

  struct MyStaticScalar: ExpressibleByUnicodeScalarLiteral {
      typealias UnicodeScalarLiteralType = StaticString
      let value: StaticString
      init(unicodeScalarLiteral value: StaticString) {
          self.value = value
      }
  }
  
  let emoji: StaticString = MyStaticScalar("\u{1F600}").value
  emoji.hasPointerRepresentation  //-> false
  emoji.isASCII                   //-> false
  emoji.unicodeScalar.value       //-> 0x1F600
  emoji.utf8CodeUnitCount         //-> Fatal error!
  emoji.utf8Start                 //-> Fatal error!

You can use the withUTF8Buffer(_:) method to access a static string’s contents, regardless of which representation the static string uses.

emoji.withUTF8Buffer { utf8 in
    utf8.count  //-> 4
    utf8[0]     //-> 0xF0
    utf8[1]     //-> 0x9F
    utf8[2]     //-> 0x98
    utf8[3]     //-> 0x80
    utf8[4]     //-> Fatal error!
}