code works in playground, but not in project

I've tried both in playground and in IOS App. Works in both.

But, I've included the code

topChoice.append(imCool) // this will fail: 1) As I type it doesn't autocomplete, and 2) fails with error "expected declaration"

in a func.

You cannot put it directly in the class ; in that case, it expects declarations only.

This works

class ViewController: UIViewController {
    struct CaptionOption {
        let emojiOption: String
        let captionphrase: String
    }
  
    override func viewDidLoad() {
        super.viewDidLoad()

        let imCool = CaptionOption(emojiOption: "  ", captionphrase: "I'm cool with that")
        let unlucky = CaptionOption(emojiOption: "  ", captionphrase: "I'm so unlucky")
        let dweeb = CaptionOption(emojiOption: "  ", captionphrase: "You're a dork")
        let run = CaptionOption(emojiOption: "  ♂️", captionphrase: "run away!")
        var topChoice = [CaptionOption]()
        var bottomChoice = [CaptionOption]()
        topChoice.append(imCool) // this will fail: 1) As I type it doesn't autocomplete, and 2) fails with error "expected declaration"
    }

This does not

class ViewController: UIViewController {
    struct CaptionOption {
        let emojiOption: String
        let captionphrase: String
    }

    let imCool = CaptionOption(emojiOption: "  ", captionphrase: "I'm cool with that")
    let unlucky = CaptionOption(emojiOption: "  ", captionphrase: "I'm so unlucky")
    let dweeb = CaptionOption(emojiOption: "  ", captionphrase: "You're a dork")
    let run = CaptionOption(emojiOption: "  ♂️", captionphrase: "run away!")
    var topChoice = [CaptionOption]()
    var bottomChoice = [CaptionOption]()
    topChoice.append(imCool) // this will fail: 1) As I type it doesn't autocomplete, and 2) fails with error "expected declaration"

    override func viewDidLoad() {
        super.viewDidLoad()
    }