使用Enumerations with Switches时,可以将关联的值绑定到变量。例如:
let x: Int? = 5
switch x {
case .some(let wrapped):
print(wrapped) //Assosiated value bound to "wrapped"
case .none:
print("nil")
}
是否有类似的方法来绑定泛型类型参数?这是我正在寻找的语义类型:
func foo(_ arg: T) {
switch arg {
case array as Array<let X>:
print("The argument is an array of \(X)")
default:
print("The argument is not an array")
}
}
答案 0 :(得分:2)
您想检查参数是否为Array?试试这个:
func foo<T>(arr: Array<T>) {
print("argument is array of \(T.self)")
switch T.self {
case is Int.Type:
print("integer array")
default:
print("Unknown type or empty")
}
}
然后你可以只将数组作为参数传递,而无需进行无用的检查。
答案 1 :(得分:1)
您可以使用Mirror
- 它的设计,而不是您正在寻找的语法,但如何:
func isItACollection(_ any: Any) -> [String : Any.Type]? {
let m = Mirror(reflecting: any)
switch m.displayStyle {
case .some(.collection):
// `.children` gives us the actual types of the elements
// This may be heterogeneous, so we spoof a Set of types
// by using a dictionary
var types: [String: Any.Type] = [:]
for (_, t) in m.children {
types["\(type(of: t))"] = type(of: t)
}
return types
default:
return nil
}
}
func test(_ a: Any) -> String {
switch isItACollection(a) {
case .some(let X):
return "The argument is an array of \(X)"
default:
return "The argument is not an array"
}
}
test([1, 2, 3]) // The argument is an array of ["Int": Swift.Int]
test([1, 2, "3"]) // The argument is an array of ["Int": Swift.Int, "String": Swift.String]
test(["1", "2", "3"]) // The argument is an array of ["String": Swift.String]
test(Set<String>()) // The argument is not an array
test([1: 2, 3: 4]) // The argument is not an array
test((1, 2, 3)) // The argument is not an array
test(3) // The argument is not an array
test("3") // The argument is not an array
test(NSObject()) // The argument is not an array
test(NSArray(array:[1, 2, 3])) // The argument is an array of ["_SwiftTypePreservingNSNumber": _SwiftTypePreservingNSNumber]
答案 2 :(得分:0)
如果你只是想知道泛型类型,你可以这样做:
func checkType<T>(_ arg: Array<T>) {
print("The argument is an Array of type \(type(of: T.self))")
}
func checkType<T>(_ arg: T) {
print("The argument is of type \(type(of: T.self))")
}
checkType([1])
checkType(1)
// The argument is an Array of type Int.Type
// The argument is of type Int.Type
但是,如果您还想绑定泛型类型持有的值:
func showValue<T>(from arg: T) {
switch arg {
case let value as Array<Any>:
print("value is \(value)")
case let value as Int:
print("value is \(value)")
default:
print("couldn't get value")
}
}
showValue(from: [1])
showValue(from: 1)
// value is [1]
// value is 1