Make statement more clear: checking object for key in dictionary - swift

Question

I have dictionary of type - [String : [MyClass]].
I have array of type MyClass, what i want is to check, whether my dictionary contain array of MyClass object for specific key. If it does, it append element to array, if not, it create new array with single element MyClass. I ended up with:
for item in items{
if let _ = dict[key] {
// Add operations if corresponding array exist
dict[key]?.append(item)
} else {
// Create array if need
dict[key] = [item]
}
}
it work but look kind of ugly, and i use optional binding for check whether array exist, but not use the result (wildcard pattern _).
Is there anyway to make that code look shorter and cleaner? Thanks.

Answer 1

First, you can test and get an existing value with optional binding,
and then append (or set) all new items:
if let oldItems = dict[key] {
dict[key] = oldItems + items
} else {
dict[key] = items
}
This can be simplified with the nil-coalescing operator ??:
dict[key] = (dict[key] ?? []) + items
In Swift 4 you can simply use the subscript method with a default value:
dict[key, default: []] += items
// Or:
dict[key, default: []].append(contentsOf: items)
Self-contained example:
var dict = ["foo": [1, 2, 3]]
dict["foo", default: []] += [4, 5]
dict["bar", default: []] += [6,7]
print(dict) // ["bar": [6, 7], "foo": [1, 2, 3, 4, 5]]

Answer 2

You can use the following implementation to avoid wildCart pattern :
import Foundation
class MyClass { }
class Apple : MyClass { }
class Ant : MyClass { }
class Ambulance : MyClass { }
class Test {
var dictionary : [String : [MyClass.Type]] = [:]
let items : [MyClass.Type] = [Apple.self, Ant.self, Ambulance.self]
let key = "a"
public func insert(key : String, items : [MyClass.Type] ) {
guard !items.isEmpty else { return }
items.forEach { (item) in
if dictionary[key] == nil {
dictionary[key] = [item]
} else {
dictionary[key]?.append(item)
}
}
}
}
let test = Test()
test.insert(key: test.key, items: test.items)
print(test.dictionary)
Output :
["a": [__lldb_expr_27.Apple, __lldb_expr_27.Ant, __lldb_expr_27.Ambulance]]