斯威夫特3之前,参数名称是类型的一部分,只要该类型的系统而言。但是,强制使用关键字名称进行适当匹配会导致使用关闭的噩梦。因此,类型系统忽略了它们,这引出了为什么它们是名字中类型的一部分的问题。
import CoreFoundation
func applyAndPrint(closure: (a: Double, b: Double) -> Double, _ a: Double, _ b: Double) {
print(a, b, closure(a: a, b: b))
}
//All these have different types, because of their different keyword parameter names.
let adder: (augend: Double, addend: Double) -> Double = { $0 + $1 }
let subtractor: (minuend: Double, subtrahend: Double) -> Double = { $0 - $1 }
let multiplier: (multiplicand: Double, multiplier: Double) -> Double = { $0 * $1 }
let divider: (dividend: Double, divisor: Double) -> Double = { $0/$1 }
let exponentiator: (base: Double, exponent: Double) -> Double = { pow($0, $1) }
let rooter: (degree: Double, Radicand: Double) -> Double = { pow($1, 1/$0) }
// Yet the type system ignores that, and all these are valid:
applyAndPrint(adder, 2, 3)
applyAndPrint(subtractor, 2, 3)
applyAndPrint(multiplier, 2, 3)
applyAndPrint(divider, 2, 3)
applyAndPrint(exponentiator, 2, 3)
applyAndPrint(rooter, 2, 3)
https://github.com/apple/swift-evolution/blob/master/proposals/0111-remove-arg-label-type-significance.md – Alexander