Closures

Toy Bin

For the following questions, we're going to be calling on the sorted(by:) function available to Arrays. Take a look in the SortingStuff.swift file. You will notice that we have a ToyBin struct, along with Ship, Book, BowlingPin, MusicCD structs. Lastly, there's a Color enum. The ToyBin has stored properties of its own being arrays of these other structs. We have ourselves a toybin that contains bins (arrays) of all of these various toys. Its our job to create functions on the ToyBin struct that will be able to sort these various bins (arrays).

(1) Create a function named sortShips(). In your implementation of this function, you will want to sort the ships stored property. How should you do that? Use the sorted(by:) function available to Arrays. This sorted(by:) function takes in as an argument a closure. Call this function on the ships stored property and implement the closure.

How should you implement this closure? Using the following conditions:

• If the name of the ship is "Titanic", it should be at the front of the list.
• They should be sorted from the oldest ships to the youngest ships (using their age).

sorted(by:) returns back a [Ship]--that is an array of Ships all sorted. Make sure to assign this return value back to the ships stored property.

(2) Create a function named sortBooks(). Similar to question #1, you will be calling sorted(by:). This time, we will be calling on the sorted(by:) function on the books stored property and assign the return value of that function call back to the books property (to mutate it!).

How should you implement the closure? Use the following conditions:

• The books should be sorted by their name property. A --> Z
• Try implementing this closure using the shorthand argument names ($0, $1, etc.)

(3) Create a function named sortBowlingPins(). Similar to the above questions, you will be calling sorted(by:). The sorted(by:) function should be called on the bowlingPins stored property. The return value should be assigned to the bowlingPins property (thus mutating it!).

How should you implement the closure? Use the following conditions:

• Each instance of BowlingPin has a color stored property of type Color. We want to sort our bowlingPins so that they form a rainbow. (meaning.. red first, orange second, yellow third, etc.). Take a look at the Color enum (notice how it's backed by a raw value). That was a hint.
• Implement this closure using shorthand argument names only.

(4) Create a function named sortMusicCDs(). Similar to the above questions, you will be calling on the sorted(by:) function. It should be called on the musicCDs stored property where the return value is assigned to the musicCDs property.

How should you implement the closure? Use the following conditions:

• The CD's should be sorted by name. In alphabetical order.
• One condition, "Drake" should be at the front of the list (no matter what).

Live without pretending, love without depending, listen without defending, speak without offending" -Drake

(5) Create a function called changeColorOfAllPins(to:) which takes in one argument called color of type Color. Ultimately, we want to change the color stored property of every BowlingPin instance in our bowlingPins array to the color parameter passed in to this function. Can you do this with a for-in loop? Yes. Should you for this problem? No--we will be using the map function instead!

Implement this function by calling the map function on our bowlingPins stored property. This function call will return back a new array (of the same type of the function thats calling it) which means it will return back a [BowlingPin] array.

When you call on map, it requires that you pass in a closure as an argument. You should look to call on changeColor(to:) (a function available to any instance of BowlingPin) within your implementation of the closure.

The return value on your map method call should be assigned to the bowlingPins stored property (thus mutating it!).

Calculator Function (advanced)

This question is optional (meaning.. it's not required). Head over to the ViewController.swift file and implement this function there.

This function should take in any amount of Doubles. As well, it will also take in a function of type (Double, Double) -> Double. If you don't know how to read that syntax, I recommend watching this video. Also, click this link and read the section titled Functions as Types.

How it will look when someone calls on this function (that you will be asked to make soon).

This is an example of calling on this function passing in three Double values.

performOperation(with: 1, 2, 3, operation: +)

This is an example of calling on the function passing in only one Double value.

performOperation(with: 1, operation: +)

You might notice that when passing in values to this function, we're able to pass in multiple values (like in the first example) without using an Array.

The function below is not how we want this function to work. This function is different in that it would be accepting of an Array of Doubles (which is not what we want).

performOperation(with: [1, 2, 3] operation: +)

How do we create a function then with the intended behavior (the first two examples)?

Click this link, scroll down and read the section titled Variadic Parameters.

.. back to the problem at hand.

Task: Create a function named performOperation(with:operatrion) that takes in two arguments. The first argument should be named numbers of type Double... (if you read the section above on Variadic Parameters, you know what this means). The other argument should be named operation of type (Double, Double) -> Double. The performOperation(with:operation) itself should return back a Double.

In your implementation, you should perform the passed in operation on each and every number.

For example:

let result = performOperation(with: 5, 2, -9, operation: -)
print(result)
// Prints "12.0"
        
let anotherResult = performOperation(with: 2, 2, 5, operation: +)
print(anotherResult)
// Prints "9.0"

Here's the kicker. In your implementation, you need to use the reduce function available to the numbers parameter. reduce is available to arrays (which is what numbers becomes being a variadic parameter). No for-in loops.