The map method takes a closure as an argument, calls it for each item in the array, and returns a mapped value for the item. The returned mapped value can be of a different type from the item's type.

The following lines declare a new getUppercasedNames method for our previously coded GameRepository class that performs the simplest map operation. The code file for the sample is included in the swift_3_oop_chapter_07_21 folder:

    open func getUppercasedNames() -> [String] { 
      return getAll().map({ game in game.name.uppercased() }) 
    } 

The getUppercasedGames parameterless method returns Array<String>, specified with the [String] shortcut. The code calls the getAll method and calls the map method for the result with a closure that returns the name value for each game converted to uppercase. This way, the map method transforms each Game instance into String with its name converted to uppercase. The result is an Array<String> array generated by the call to the map method.

The following line uses the GameRepository instance called gameRepository to call the previously added getUppercasedNames method and then chains a call to forEach to print all the game names converted to uppercase strings. The code file for the sample is included in the swift_3_oop_chapter_07_21 folder:

    gameRepository.getUppercasedNames().forEach( { print($0) }) 

The following lines show the output generated by the preceding code:

INVADERS 2017
MINECRAFT
MINECRAFT STORY MODE
SOCCER WARRIORS
THE WALKING DEAD STORIES
ONCE UPON A TIME IN WONDERLAND
CARS FOREVER
JAKE & PETER PAN
KONG STRIKES BACK
MARIO KART 2017

The following code shows another version of the getUppercasedNames method, which is equivalent and produces the same results. The code file for the sample is included in the swift_3_oop_chapter_07_22 folder:

    open func getUppercasedNames() -> [String] { 
      return getAll().map({ 
        (game: Game) -> String in 
        game.name.uppercased() 
      }) 
    } 

The following code shows another version of the getUppercasedNames method, which is equivalent and produces the same results. The code file for the sample is included in the swift_3_oop_chapter_07_23 folder:

    open func getUppercasedNames() -> [String] { 
      return getAll().map( { $0.name.uppercased() }) 
    }

Swift supports tuples that group multiple values into a single compound value. The following lines declare a new getUppercasedAndLowercasedNames method for our previously coded GameRepository class, which performs a map operation that returns a tuple, specifically, a tuple that groups two string values into a single compound value. The code file for the sample is included in the swift_3_oop_chapter_07_23 folder:

    open func getUppercasedAndLowercasedNames() -> [(upper: String, 
    lower: String)] { 
      return getAll().map({ 
        game -> (String, String) in 
        (game.name.uppercased(), game.name.lowercased()) 
      }) 
    } 

The getUppercasedAndLowercasedNames parameterless method returns a tuple with two named String values: [(upper: String, lower: String). The first string element in the tuple is named upper, and the second one is named lower. The code calls the getAll and map method for the result with a closure that returns a tuple with the first element equal to the name value for each game converted to uppercase and the second element with the value converted to lower case. This way, the map method transforms each Game instance into a (String, String) tuple with its name converted to uppercase and lowercase and stored in a compound value. The result is (String, String) generated by the call to the map method. The method declaration specifies names for each element in the returned tuple, so we will be able to access its members through these specified names.

The following line uses the GameRepository instance called gameRepository to call the previously added getUppercasedAndLowercasedNames method and then chains a call to forEach to print the upper and lower elements of the tuple separated by a hyphen. The code file for the sample is included in the swift_3_oop_chapter_07_23 folder:

    gameRepository.getUppercasedAndLowercasedNames().forEach( { 
    print($0.upper, " - ", $0.lower) }) 

The following lines show the output generated by the preceding code:

INVADERS 2017  -  invaders 2017

MINECRAFT  -  minecraft

MINECRAFT STORY MODE  -  minecraft story mode

SOCCER WARRIORS  -  soccer warriors

THE WALKING DEAD STORIES  -  the walking dead stories

ONCE UPON A TIME IN WONDERLAND  -  once upon a time in wonderland

CARS FOREVER  -  cars forever

JAKE & PETER PAN  -  jake & peter pan

KONG STRIKES BACK  -  kong strikes back

MARIO KART 2017  -  mario kart 2017

The following lines would produce the same results by accessing the tuple elements with .0 and .1 for the first and second elements instead of using the upper and lower names. The code file for the sample is included in the swift_3_oop_chapter_07_24 folder:

    gameRepository.getUppercasedAndLowercasedNames().forEach( { 
    print($0.0, " - ", $0.1) })

We can also easily iterate through the upper and lower pairs using a for loop. The code file for the sample is included in the swift_3_oop_chapter_07_25 folder:

    for (upper, lower) in 
    gameRepository.getUppercasedAndLowercasedNames() { 
      print("UPPER: (upper), lower: (lower)") 
    } 

The next lines show the results of executing the previous for loop:

UPPER: INVADERS 2017, lower: invaders 2017

UPPER: MINECRAFT, lower: minecraft

UPPER: MINECRAFT STORY MODE, lower: minecraft story mode

UPPER: SOCCER WARRIORS, lower: soccer warriors

UPPER: THE WALKING DEAD STORIES, lower: the walking dead stories

UPPER: ONCE UPON A TIME IN WONDERLAND, lower: once upon a time in wonderland

UPPER: CARS FOREVER, lower: cars forever

UPPER: JAKE & PETER PAN, lower: jake & peter pan

UPPER: KONG STRIKES BACK, lower: kong strikes back

UPPER: MARIO KART 2017, lower: mario kart 2017