Swift中运算符' - '与'abs()'的模糊使用

我正在尝试执行以下操作:

var i = -(abs(-3))

要么

var i = -abs(-3)

要么

var i = -abs(3)

要么

var i = -(abs(3))

但我得到一个错误,说使用减号是模棱两可的.为什么？

这对我来说看起来像编译器错误,文字的类型3 应该是Int.但是编译器抱怨道

error: ambiguous use of operator '-'
var i = -(abs(-3))
        ^
Swift.-:2:20: note: found this candidate
prefix public func -(x: Float) -> Float
                   ^
Swift.-:2:20: note: found this candidate
prefix public func -(x: Double) -> Double
                   ^
Swift.-:2:20: note: found this candidate
prefix public func -(x: Float80) -> Float80
                   ^
CoreGraphics.-:2:20: note: found this candidate
prefix public func -(x: CGFloat) -> CGFloat

您可以使用显式Intas参数来解决它:

var i = -(abs(-Int(3)))

或者在结果上使用类型注释:

var i : Int = -(abs(-3))

正如@vacawama所注意到的,还有更多可能的解决方案.转换任何子表达式Int使编译器开心:

var i1 = -(abs(-(3 as Int)))
var i2 = -(abs((-3) as Int))
var i3 = -(abs(-3) as Int)
var i4 = -(abs(-3)) as Int