使用下标访问字典键的值。这将返回一个可选：

let apple: String? = companies["AAPL"]

要么

if let apple = companies["AAPL"] {
    // ...
}

您还可以枚举所有键和值：

var companies = ["AAPL" : "Apple Inc", "GOOG" : "Google Inc", "AMZN" : "Amazon.com, Inc", "FB" : "Facebook Inc"]

for (key, value) in companies {
    print("\(key) -> \(value)")
}

或枚举所有值：

for value in Array(companies.values) {
    print("\(value)")
}