f#泛型类型上的泛型单位

是否可以定义一个通用于数据类型和度量单位的函数？例如，我想做什么，但没有编译（虽然即使没有度量单位也不会，但我相信我表达了我想做的事情）：

我知道，对于这个特殊情况，我可以使用

let dropUnit (x : float<_>) = (float) x

让dropUnit（x:float）=（float）x

---

但是在写上述内容时，我开始思考一般情况。

关于如何编写

isValidUnitValue

函数的具体问题，答案是：

let inline isValidUnitValue myUnit = myUnit > LanguagePrimitives.GenericZero

所以你不需要定义一个歧视性的联盟

关于最初的问题，是否可以定义一个既通用于数据类型又通用于度量单位（如

dropUnit

）的函数，简短的回答是否定的。如果存在这样的函数，它将有一个签名，如

'a`）=
让ux=x*（LanguagePrimitives.GenericOne:'Num）
重新键入x:'Num

---

这类似于2），但不需要类型注释。其局限性在于它仅适用于数字类型，但通常情况下，这是计量单位的使用情况。

另一种选择是使用内联函数来伪造接口。

let isValidUnitValue myUnit =
   match myUnit with
       | Weight(x) -> (dropUnit x) > 0.
       | Volume(x) -> (dropUnit x) > 0.

let dropUnit (x : float<_>) = (float) x

let inline isValidUnitValue myUnit = myUnit > LanguagePrimitives.GenericZero

    type UnitDropper = 
        static member drop (x:sbyte<_>  ) = sbyte   x
        static member drop (x:int16<_>  ) = int16   x
        static member drop (x:int<_>    ) = int     x
        static member drop (x:int64<_>  ) = int64   x
        static member drop (x:decimal<_>) = decimal x
        static member drop (x:float32<_>) = float32 x
        static member drop (x:float<_>  ) = float   x

    [<Measure>] type m
    let x = UnitDropper.drop 2<m> + 3

> let inline dropUnitAndAdd3 x = UnitDropper.drop x + 3 ;;
-> error FS0041: A unique overload for method 'drop' could not be determined ...

    let inline retype (x:'a) : 'b = (# "" x : 'b #)

    [<Measure>] type m
    let x = retype 2<m> + 3
    let inline dropUnitAndAdd3 x = retype x + 3

let y = retype 2.0<m> + 3

    type DropUnit = DropUnit with
        static member ($) (DropUnit, x:sbyte<_>  ) = sbyte   x
        static member ($) (DropUnit, x:int16<_>  ) = int16   x
        static member ($) (DropUnit, x:int<_>    ) = int     x
        static member ($) (DropUnit, x:int64<_>  ) = int64   x
        static member ($) (DropUnit, x:decimal<_>) = decimal x
        static member ($) (DropUnit, x:float32<_>) = float32 x
        static member ($) (DropUnit, x:float<_>  ) = float   x

    let inline dropUnit x = DropUnit $ x

    [<Measure>] type m
    let x = dropUnit 2<m>   + 3
    let inline dropUnitAndAdd3 x = dropUnit x + 3
    let y = dropUnit 2.0<m> + 3   //fails at compile-time

    type MyNumericType<[<Measure 'U>]> =
        ...
        static member dropUoM (x:MyNumericType<_>) : MyNumericType = ...
        static member ($) (DropUnit, x:MyNumericType<_>) = MyNumericType.dropUoM(x)

    let inline retype (x: 'T) : 'U = (# "" x: 'U #)
    let inline stripUoM (x: '``Num<'M>``) =
        let _ = x * (LanguagePrimitives.GenericOne : 'Num)
        retype x :'Num