f＃将字符串解析为颜色

Question

type circle = { X : int; Y : int; Diameter : int; Color : Color}
let mutable clickedCircle = { X = 0; Y = 0; Diameter = 0; Color = Color.White}

let txtBoxVal4 = System.Enum.Parse(typeof<Color>,txtBox2.Text)
clickedCircle <- {X = txtBoxVal2; Y = txtBoxVal3; Diameter = txtBoxVal1; Color = txtBoxVal4}

I am trying to parse a textbox.text into a color. From this code i get the error:

Error   1   This expression was expected to have type
Color    
but here has type
obj 

Quite new to F# and not to sure about the syntax. The error comes at

"Color = txtBoxVal4"

Answer 1

System.Enum.Parse returns an obj type that you need to cast to the enum type. You can do that using :?> or downcast . In your case the type is known so you can use downcast .

See the Casting and Conversions docs for more.

clickedCircle <- {X = txtBoxVal2; Y = txtBoxVal3; Diameter = txtBoxVal1; Color = downcast txtBoxVal4}

Answer 2

A wrapper function for Enum.Parse could make good use of the enum constraint and eliminate the need for unboxing at the call site.

module Enum =
  let parse<'T, 'U when 'T : enum<'U>> value = Enum.Parse(typeof<'T>, value) :?> 'T

let color = Enum.parse "Black"