IS
let a1 = ["a": 1, "b": 2, "c": 3]
let a2 = ["a": 10, "d": 30]
print(a1.merging(a2) { q, w in w })
func + <K, V> (left: [K: V], right: [K: V]) -> [K: V] {
var result: [K: V] = left
for (k, v) in right {
result[k] = v
}
return result
}
print(a1 + a2)