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)")
}
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