F＃测量单位，不丢失测量类型的铸造 [英] F# Unit of Measure, Casting without losing the measure type

问题描述

是否有内置版本的类型转换函数保留单位，如果不是我将如何使他们？因此，例如，使用这个代码如何将intWithSecondsMeasure转换为浮点数，而不会丢失度量或乘以 1.0< s> ？

Is there built in version of the type casting functions that preserves units and if not how would I make them? So for example with this code how would I cast intWithSecondsMeasure to a float without losing the measure or multiplying by 1.0<s>?

[<Measure>] type s
let intWithSecondsMeasure = 1<s>
let justAFloat = float intWithSecondsMeasure 

推荐答案

由@kvb提供肯定工作，但我不想使用 unbox 运算符进行此转换。有一个更好，内置的方式，我认为应该编译为一个NOP到IL（我没有检查，但是unbox可能会最终作为一个 unbox 在IL中的指令，因此添加一个运行时类型检查。）

The answer provided by @kvb certainly works, but I'd prefer not to use the unbox operator for this conversion. There's a better, built in way that I think should be compiled as a NOP to IL (I haven't checked but unbox is probably going to end up as a unbox instruction in IL and thus adds a runtime type check).

在F＃中进行单位转换的首选方法是 LanguagePrimitives。 TypeWithMeasure （ MSDN ）

The preferred way to do unit conversions in F# is LanguagePrimitives.TypeWithMeasure (MSDN).

let inline float32toFloat (x:float32<'u>) : float<'u> = 
    x |> float |> LanguagePrimitives.FloatWithMeasure

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