确保计算中的一致单位

度量单位是可以添加到浮点数或整数的附加类型注释。它们可用于在编译时验证计算是否始终使用单位。

要定义注释：

[<Measure>] type m // meters
[<Measure>] type s // seconds
[<Measure>] type accel = m/s^2 // acceleration defined as meters per second squared

定义后，注释可用于验证表达式是否产生预期类型。

// Compile-time checking that this function will return meters, since (m/s^2) * (s^2) -> m
// Therefore we know units were used properly in the calculation.
let freeFallDistance (time:float<s>) : float<m> = 
    0.5 * 9.8<accel> * (time*time)    

// It is also made explicit at the call site, so we know that the parameter passed should be in seconds
let dist:float<m> = freeFallDistance 3.0<s>
printfn "%f" dist