Swift - Strings

Strings in Swift 4 are an ordered collection of characters, such as "Hello, World!" and they are represented by the Swift 4 data type String, which in turn represents a collection of values of Character type.

Create a String

You can create a String either by using a string literal or creating an instance of a String class as follows −

// String creation using String literal  var stringA = "Hello,
 Swift 4!"  print( stringA )
 
// String creation using String instance  var stringB = String
("Hello, Swift 4!")  print( stringB )    

//Multiple line string    let stringC = """  Hey this is a  
example of multiple Line  string by tutorialsPoint     """  
print(stringC)

When the above code is compiled and executed, it produces the following result

Hello, Swift 4!  
Hello, Swift 4!  
Hey this is a example of multiple Line string by tutorialsPoint  

Empty String

You can create an empty String either by using an empty string literal or creating an instance of String class as shown below. You can also check whether a string is empty or not using the Boolean property isEmpty.

// Empty string creation using String literal  var stringA = ""    
 
if stringA.isEmpty {     
   print( "stringA is empty" )  
} else {  
   print( "stringA is not empty" )  
}    
              

// Empty string creation using String instance  
let stringB = String()    

if stringB.isEmpty {
     print( "stringB is empty" )  
} else {
     print( "stringB is not empty" ) 
 }

When the above code is compiled and executed, it produces the following result −

stringA is empty 
stringB is empty  

String Constants

You can specify whether your String can be modified (or mutated) by assigning it to a variable, or it will be constant by assigning it to a constant using let keyword as shown below −

// stringA can be modified 
 var stringA = "Hello, Swift 4!" 
 stringA + = "--Readers--" 
 print( stringA ) 
 
// stringB can not be modified 
 let stringB = String("Hello, Swift 4!") 
 stringB + = "--Readers--" 
 print( stringB )

When the above code is compiled and executed, it produces the following result −

Playground execution failed: error: <EXPR>:10:1: error: 
'String'is not  convertible to '@lvalue UInt8' 
 stringB + = "--Readers--"  

String Interpolation

String interpolation is a way to construct a new String value from a mix of constants, variables, literals, and expressions by including their values inside a string literal.

Each item (variable or constant) that you insert into the string literal is wrapped in a pair of parentheses, prefixed by a backslash. Here is a simple example −

var varA = 20 
let constA = 100 
var varC:Float = 20.0 
 
var stringA = "\(varA) times \(constA)is equal to \(varC * 100)"
print( stringA )

When the above code is compiled and executed, it produces the following result −

20 times 100 is equal to 2000.0

String Concatenation

You can use the + operator to concatenate two strings or a string and a character, or two characters. Here is a simple example −

let constA = "Hello,"
let constB = "World!"
 
var stringA = constA + constB 
print( stringA )

When the above code is compiled and executed, it produces the following result −

Hello,World!  

String Length

Swift 4 strings do not have a length property, but you can use the global count() function to count the number of characters in a string. Here is a simple example −

var varA = "Hello, Swift 4!" 

print( "\(varA), length is \((varA.count))" )

When the above code is compiled and executed, it produces the following result −

Hello, Swift 4!, length is 15  

String Comparison

You can use the == operator to compare two strings variables or constants. Here is a simple example −

var varA = "Hello, Swift 4!"
var varB = "Hello, World!" 

if varA == varB {   
   print( "\(varA) and \(varB) are equal" ) 
 }  else { 
    print( "\(varA) and \(varB) are not equal" ) 
 }

When the above code is compiled and executed, it produces the following result −

Hello, Swift 4! and Hello, World! are not equal  

String Iterating

Strings are again a collection of values in swift 4, so we can iterate over string using loops. −

for chars in "ThisString" {  
   print(chars, terminator: " ") 
 }

When the above code is compiled and executed, it produces the following result −

T h i s S t r i n g  

Unicode Strings

You can access a UTF-8 and UTF-16 representation of a String by iterating over its utf8 and utf16 properties as demonstrated in the following example −

var unicodeString = "Dog???" 
 
   print("UTF-8 Codes: ")  
 for code in unicodeString.utf8 {  
   print("\(code) ") 
 }  
 
  print("\n")  
 
 
 print("UTF-16 Codes: ") 
 for code in unicodeString.utf16 { 
    print("\(code) ") 
 }

When the above code is compiled and executed, it produces the following result −

UTF-8 Codes: 
  68 
  111 
  103  
  63 
  63 
  63 
  
UTF-16 Codes:
  68
  111 
  103 
  63 
  63 
  63   

String Functions & Operators

Swift 4 supports a wide range of methods and operators related to Strings −

Sr.No	Functions/Operators & Purpose
1	isEmpty A Boolean value that determines whether a string is empty or not.
2	hasPrefix(prefix: String) Function to check whether a given parameter string exists as a prefix of the string or not.
3	hasSuffix(suffix: String) Function to check whether a given parameter string exists as a suffix of the string or not.
4	toInt() Function to convert numeric String value into Integer.
5	count() Global function to count the number of Characters in a string.
6	utf8 Property to return a UTF-8 representation of a string.
7	utf16 Property to return a UTF-16 representation of a string.
8	unicodeScalars Property to return a Unicode Scalar representation of a string.
9	+ Operator to concatenate two strings, or a string and a character, or two characters.
10	+= Operator to append a string or character to an existing string.
11	== Operator to determine the equality of two strings.
12	< Operator to perform a lexicographical comparison to determine whether one string evaluates as less than another.
13	startIndex To get the value at starting index of string.
14	endIndex To get the value at ending index of string.
15	Indices To access the indeces one by one. i.e all the characters of string one by one.
16	insert("Value", at: position) To insert a value at a position.
17	remove(at: position) removeSubrange(range) to remove a value at a position, or to remove a range of values from string.
18	reversed() returns the reverse of a string