Dictionary.swift

struct Placeholder<Key, Value where Key: Hashable> {
    var values: [(Key, Value)] = []
    
    func firstValue(matchingKey key: Key) -> Value? {
        return values.lazy.filter({ $0.0 == key }).first?.1
    }
}

struct Dictionary<Key, Value where Key: Hashable> {
    private var storage = Array(count: 8, repeatedValue: Placeholder<Key, Value>())
    
    subscript(key: Key) -> Value? {
        get {
            let position = abs(key.hashValue) % storage.count
            return storage[position].firstValue(matchingKey: key)
        }
        set {
            guard let value = newValue else { return }
            let position = abs(key.hashValue) % storage.count
            storage[position].values.append((key, value))
        }
    }
}

var d = Dictionary<String, String>()
d["123"] = "asdf"
d["123"]