String Theory

let a = "I am a string"

A string is an ordered-collection of characters. The String type in Swift is similar in many ways to the NSString class from Objective-C. In fact, the entire API for NSString is available to the String type in Swift. One difference between Objective-C and Swift is that in Swift a string is mutable or not based on whether it is a variable or constant, whereas Objective-C used the NSMutableString class. Another difference is that in Swift, String is a value type; meaning that the value is copied whenever a string is passed to a function or method, or assigned to a constant or variable. In Objective-C, the NSString would pass a reference to a single NSString object.

/* To create an empty String, the following two options can be used */
var empty1 = ""
var empty1 = String()

// To concatenate Strings, the + sign can be used
var empty1 = "Hello"
var string1 = empty1 + " World!"

• utf16Count: Swift does not use a length property like NSString from Objective-C, but instead uses a utf16Count property to return the number of Unicode characters.
• isEmpty: read-only property that returns a Bool, stating whether or not the String has a value.

// using the utf16Count property to return the number of Unicode characters in a String:
var greeting: String = "Hello. How are you?"
println("There are \(greetings.utf16Count) Unicode characters in the greeting String")
//prints "There are 19 Unicode characters in the greeting String"


//using the isEmpty property to determine if a String has a value
if greeting.isEmpty{
 println("The greeting String is Empty")
} else {
 println("The greeting String has values")
}

• append(c: Character): adds a Character value to the end of an existing String.
• append(x: UnicodeScalar): adds a Unicode Scalar to the end of an existing String.
• capitalizedString: returns the String with each new word of the String capitalized.
• lowercaseString: returns the String with each Unicode character lowercase.
• uppercaseString: returns the String with each Unicode character uppercase.
• caseInsensitiveCompare(<aString: String>): calls the compare method with the options set to NSCaseInsensitiveSearch
• compare(<aString: String>, options: <NSStringCompareOptions>, range: <Range<String.Index>?>, locale: <NSLocale?>): does a comparison based off specified options returning results in lexical order for a range.
• insert(<newElement: Character>, atIndex: <String.Index&rt;): inserts a Character at a specified index in the String.
• substringFromIndex(<index: String.Index&rt;): returns part of a String from the provided index to the end of the String.
• substringToIndex(<index: String.Index&rt;): returns part of a String from the start of the String to the provided index.
• substringWithRange(<aRange: Range<String.Index>>): returns part of a String based off of the provided range.

//use the append() method to add Character or UnicodeScalar to the end of a String
var test = "this is a test!"
var charca: Character = "a"
var unic: UnicodeScalar = "b"
test.append(charca)
println(test)
//prints 'this is a test!a'
test.append(unic)
println(test)
//prints 'this is a test!ab'

//use the capitalizedString, lowercaseString, and uppercaseString methods to change a String
var test2 = "this IS not A test!"
println("\(test2.capitalizedString)")
//prints 'This Is Not A Test!'
println("\(test2.lowercaseString)")
//prints 'this is not a test!'
println("\(test2.uppercaseString)")
//prints 'THIS IS NOT A TEST!'

//use substringFromIndex and substringToIndex to return part of a String
var test3 = "Why do we have so many tests?"
var StrIndex = advance(test3.startIndex, 6)
println(test3.substringFromIndex(StrIndex))
//prints ' we have so many tests?'
println(test3.substringToIndex(StrIndex))
//prints 'Why do'

• + : the Addition Assignment operator can be used to concatenate two Strings.
• += : the Addition and Equal Assignment operator will add the value on the right side of the operator to the original String.
• == : the Equal To operator performs a comparison determining if the two Strings are equal. This does NOT do a byte to byte comparison like NSString's isEqualToString method.
• != : the Not Equal To operator performs a comparison determining if the two Strings are not equal. This does NOT do a byte to byte comparison.
• <, <=, >, >= : these comparison operators perform a comparison based on the Unicode Collation Algorithm to determine the order of Strings.

//using the += operator to add a new String to the existing String
var test = "Hello... "
test += "Miss Lady"
//the String is now 'Hello... Miss Lady'

//using the less than and greater than operators to compare two Strings
var str1 = "hello" var str2 = "goodnight" println(str1 < str2) //prints false
println(str1 > str2) //prints true