import UIKit let numbers = (1...5).map(String.init) print(numbers) // ["1", "2", "3", "4", "5"] var a: [String] = [] // No Error a = Array(numbers.prefix(3)).map { $0 } print(a) // ["1", "2", "3"] // No Error let arraySlice: ArraySlice<String> = numbers.prefix(3) a = arraySlice.map { $0 } print(a) // ["1", "2", "3"] // Error（error: ambiguous use of 'prefix'）→ なぜエラーに？ // a = numbers.prefix(3).map { $0 }