Can Swift convert a class / struct data into dictionary?

You can just add a computed property to your struct to return a Dictionary with your values. Note that Swift native dictionary type doesn’t have any method called value(forKey:). You would need to cast your Dictionary to NSDictionary:

struct Test {
    let name: String
    let age: Int
    let height: Double
    var dictionary: [String: Any] {
        return ["name": name,
                "age": age,
                "height": height]
    }
    var nsDictionary: NSDictionary {
        return dictionary as NSDictionary
    }
}

You can also extend Encodable protocol as suggested at the linked answer posted by @ColGraff to make it universal to all Encodable structs:

struct JSON {
    static let encoder = JSONEncoder()
}
extension Encodable {
    subscript(key: String) -> Any? {
        return dictionary[key]
    }
    var dictionary: [String: Any] {
        return (try? JSONSerialization.jsonObject(with: JSON.encoder.encode(self))) as? [String: Any] ?? [:]
    }
}

struct Test: Codable {
    let name: String
    let age: Int
    let height: Double
}

let test = Test(name: "Alex", age: 30, height: 170)
test["name"]    // Alex
test["age"]     // 30
test["height"]  // 170