List in dictionary as a template definition - arrays

Question

I'm using arrays which are stored in a dictionray for fast access. Because I need this logic for different data types, I like to define it as a template, but I don't have any idea how to pass types. In my own description it should look like this:
struct KeyList {
let key : MyType1
var list = [MyType2]()
init(key : MyType1, value : MyType2) {
self.key = key
self.list.append(value)
}
}
var dicList = [String: KeyList]()
value = ...of MyType2
key = ... of MyType1
if dicList[key] == nil {
// new entry
dicList[key] = KeyList(key: key, value: value)
}
else {
// add it to existing list
dicList[key]!.list.append(value)
}
}
But I want to use Swift 3. Any idea, if this is possible?

Answer 1

You'll need a couple of things:
generics
encapsulation
Snippet
Here's an example
struct Container<Key, Value> where Key: Hashable {
private var dict: [Key:[Value]] = [:]
func list(by key: Key) -> [Value]? {
return dict[key]
}
mutating func add(value: Value, to key: Key) {
dict[key] = (dict[key] ?? []) + [value]
}
}
Usage
Now you can create a Container specifying the Key and the Value types
var container = Container<String, Int>()
container.add(value: 1, to: "a")
container.add(value: 2, to: "a")
container.list(by: "a") // [1, 2]
Update
You asked in the comments how to implement a remove functionality. In this case the Value needs to be Equatable. Here's the code
struct Container<Key, Value> where Key: Hashable, Value: Equatable {
private var dict: [Key:[Value]] = [:]
func list(by key: Key) -> [Value]? {
return dict[key]
}
mutating func add(value: Value, to key: Key) {
dict[key] = (dict[key] ?? []) + [value]
}
mutating func remove(value: Value, from key: Key) {
guard var list = dict[key] else { return }
guard let index = list.index(of: value) else { return }
list.remove(at: index)
dict[key] = list
}
}