在使用Measurement时，我无法返回Double，即使它应该返回Double

Question

试图使用Swift的Measurements创建一个函数，该函数返回Double。我显然是头脑发热，不明白为什么，尽管我的函数正在调用以返回一个double，但它给了我以下错误：Cannot convert return expression of type 'Measurement<UnitLength>' to return type 'Double'

func convertImperialHeightToCM() -> Double {
// User input of Feet, forcing unwrap will likely fuck this up...
let convertFeetToCm = Measurement(value: userData!.userHeightFeet, unit: UnitLength.feet)
let feetToCentimeters = convertFeetToCm.converted(to: UnitLength.centimeters)
// User input of Inches, forcing upwrap will likely fuck this up...
let convertInchesToCm = Measurement(value: userData!.userHeightInches, unit: UnitLength.inches)
let inchesToCentimeters = convertInchesToCm.converted(to: UnitLength.centimeters)
// Compute this shit and whip the numbers into one... 
let addUpCentimeters = feetToCentimeters + inchesToCentimeters

return addUpCentimeters
}

然后，我稍后也会在其他函数中调用这个函数(可能会生成一个嵌套函数，但将它们分解以帮助进行测试，另外，我是一个noob

Answer 1

问题是addUpCenmeters是一个测量单位，而不是双精度。因此，您有两个选项，要么返回该单位，要么调用addUpCentimeers.value来获得实际的双倍值。

Answer 2

您可以使用.value到英尺到厘米和英寸到厘米从测量获得双倍值。

func convertImperialHeightToCM() -> Double {
// User input of Feet, forcing unwrap will likely fuck this up...
let convertFeetToCm = Measurement(value: userData!.userHeightFeet, unit: UnitLength.feet)
let feetToCentimeters = convertFeetToCm.converted(to: UnitLength.centimeters).value
// User input of Inches, forcing upwrap will likely fuck this up...
let convertInchesToCm = Measurement(value: userData!.userHeightInches, unit: UnitLength.inches)
let inchesToCentimeters = convertInchesToCm.converted(to: UnitLength.centimeters).value
// Compute this shit and whip the numbers into one... 
let addUpCentimeters = feetToCentimeters + inchesToCentimeters

return addUpCentimeters
}