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我的理解是，'as？'並作爲！'運算符是向下轉換的，「as」用於上傳，消歧，橋接和模式匹配。但是在模式匹配過程中，'any'類型的'thing'被轉換並且dowoncasted爲 - 例如 - someInt作爲Int。爲什麼語法不是'as？'而不是'as'？在這種情況下，我很困惑爲什麼模式匹配與類型轉換有區別？模式匹配和類型鑄造之間的區別
var things = [Any]()
things.append(0)
things.append(0.0)
things.append(42)
things.append(3.14159)
things.append("hello")
things.append((3.0, 5.0))
things.append({ (name: String) -> String in "Hello, \(name)" })
for thing in things {
switch thing {
case 0 as Int:
print("zero as an Int")
case 0 as Double:
print("zero as a Double")
case let someInt as Int:
print("an integer value of \(someInt)")
case let someDouble as Double where someDouble > 0:
print("a positive double value of \(someDouble)")
case is Double:
print("some other double value that I don't want to print")
case let someString as String:
print("a string value of \"\(someString)\"")
case let (x, y) as (Double, Double):
print("an (x, y) point at \(x), \(y)")
case let stringConverter as (String) -> String:
print(stringConverter("Michael"))
default:
print("something else")
}
}