使用 Math.Round 和计量单位

Question

我正在尝试在函数中使用 Math.Round 来四舍五入货币金额，如下所示：

let calculateTaxablePayToDate previousPayToDate taxablePayThisMonth =
    taxablePayThisMonth
    |> fun (x:decimal) -> Math.Round(x)
    |> fun x -> x + previousPayToDate

我传递的类型都是 decimal<GBP> 类型。当我尝试通过函数运行它们时，虽然我得到：

This expression was expected to have type
decimal but here has type
int<GBP>

如何在附有度量单位的图形上使用 Math.Round？

Answer 1

Math.Round 需要原始值，而不是度量值。您可以将其包装在度量类型的通用函数中：

open System
open Microsoft.FSharp.Core.LanguagePrimitives

let roundMeasure<[<Measure>]'u>(x: decimal<'u>): decimal<'u> = Math.Round(decimal x) |> DecimalWithMeasure

然后你应该能够做到：

let calculateTaxablePayToDate previousPayToDate taxablePayThisMonth =
        taxablePayThisMonth |> roundMeasure |> fun x -> x + previousPayToDate

或

let calculateTaxablePayToDate previousPayToDate taxablePayThisMonth =
    previousPayToDate + (roundMeasure taxablePayThisMonth)

使用 Math.Round 和计量单位

Using Math.Round with a Unit of Measure

f#

units-of-measurement