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iOS Swift Collections and Control Flow Introduction to Collections Working With Arrays

poorly worded question: concatenate two arrays and rename the resulting expression with the same name as original?

I understand the concept of concatenating two arrays, but I am lost as to how to rename the result the same as one of the originals. It seems like circular logic.

How can a + b = a ?

I found this example on stack overflow: let array1 = [1, 2, 3] let array2 = [4, 5, 6]

let flattenArray = array1 + array2 print(flattenArray) // prints [1, 2, 3, 4, 5, 6]

// Enter your code below
var arrayOfInts: [Int] = [0, 1, 2, 3, 4, 5]

4 Answers

Jhoan Arango
Jhoan Arango
14,575 Points


This is simple, once you have created an array of Ints that hold six values, you should then re-use the arrayOfInts and concatenate a new array with one value in it.

var arrayOfInts: [Int] = [1,2,3,4,5,6]

arrayOfInts.append(7) // We use the append method
arrayOfInts = arrayOfInts + [8] // Then we use the arrayOfInts and concatenate a new array with one value in it

Hope this helps

It wouldn't be a + b = a. It would be a = a + b or shorthand a += b. Keep in mind it is an assignment not an equation.

Shorthand for the challenge might be:

arrayOfInts += [7]

Thanks. I still struggle with the logic of what seems like a circular reference, but with the guiding of your example, I can accept the idea that the compiler will use the old value of arrayOfInts in the concatenation. I appreciate the help!

You will see this all the time - especially in loops. What is on the right hand side is evaluated then assigned to the left hand side.

A JavaScript example:

var i;
for (i = 0; i < 10; i++) {

could also be written:

var i;
for (i = 0; i < 10; i = i + 1) {


var i;
for (i = 0; i < 10; i += 1) {

Thanks! visualizing the code as "right hand side" and "left hand side" is helpful. Now I understand how a = a + b