Accessing a dictionary for use in the fizzbuzz exercise

Question

Finally found what I needed after much trial, error, corrections from xcode, red herrings, and hair pulling.

But I'd like to understand the reason for the syntax.

I wanted to use a dictionary in my assignment, and while putting values into them is quite straightforward, getting them back out the same way they were before was not.

Apple's documentation had a bunch to say on updating and removing, but I didn't see much on simply accessing/displaying.

For the record, my code is

var fizzbuzzier = [3: [true:"Fizz", false: ""], 5: [true:"Buzz", false: ""]]
for n in 1...21 {
    if n % 3 == 0 || n % 5 == 0 {
        println("\(fizzbuzzier[3]![Bool(n % 3 == 0)]!)\(fizzbuzzier[5]![Bool(n % 5 == 0)]!)")
    }
}

I also came up with

var fizzbuzzier = [3: [true:"Fizz", false: ""], 5: [true:"Buzz", false: ""]]
for n in 1...21 {
    if n % 3 == 0 || n % 5 == 0 {
        for i in fizzbuzzier {
            print("\(i.1[Bool(n % i.0 == 0)]!)")
        }
        println()
    }
} // EDIT: Just realized that this results in "BuzzFizz" when both criteria are met.  Have I made a mistake, or is it iterating through in reverse order?


//More trial and error, I could fix it with:
//
//for i in [3,5] {
//            print("\(fizzbuzzier[i]![Bool(n % i.0 == 0)]!)")
//        }

but this was a bigger departure from what I'd already learned (it was the result of one of the trials/errors)

So why is it, I can create a dictionary with

var thing = [1:"one"]   //[1: "one"]

add to it with

thing[2] = "two"         //{Some "two"} <-- same phenomenon, but results in thing == [1: "one", 2: "two"]

display it normally with

thing         //[1: "one", 2: "two"]

but if I type

thing[1]         //{Some "one"}

I get {Some "one"}, which is not simply a different way of displaying it in the editor, but is in fact some other kind of object?

In order to access it, I need to type

thing[1]!         //"one"

with an ! after the [index]

Why does it change to something else once you access it directly?

Answer 1 · 2014-11-13T14:05:44Z

November 13, 2014 2:05pm

You have to add an exclamation mark because accessing a dictionary returns an optional value. That way you can check if an item actually exists. In your examples you just assume/know that the items exist, but in reality you often want to make sure that the item exists before you use it.

Check this code. It creates your dictionary and then safely prints the value of thing[1]. Play around with it, rename the key '1' to see how it acts in case of a missing key:

var thing = [1:"one"]
thing[2] = "two"

if let possibleThing = thing[1] {
  println(possibleThing)
} else {
  println("The item does not exist")
}

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Kathleen Loden

Kathleen Loden

Accessing a dictionary for use in the fizzbuzz exercise

1 Answer

luckyluckyluke

luckyluckyluke