f# - F# 中的反射和模式匹配

Question

我正在尝试在给定 F# 类型的情况下创建原始值。代码如下所示，但不起作用。我将不胜感激所有帮助并提前致谢。

open System

let getvalue (t: Type) (v: string) : obj =
    match box t with
    | :? int    ->  let r = (int) v
                    box r
    | :? byte   ->  let r = (byte) v
                    box r
    | :? sbyte  ->  let r = (sbyte) v
                    box r
    | :? int16  ->  let r = (int16) v
                    box r
    | :? uint32 ->  let r = (uint32) v
                    box r
    | :? int64 ->   let r = (int64) v
                    box r
    | :? uint64 ->  let r = (uint64) v
                    box r
    | :? double ->  let r = (double) v
                    box r
    | :? float32 -> let r = (float32) v
                    box r
    | :? decimal -> let r = (decimal) v
                    box r
    | :? char ->    let r = (char) v
                    box r
    | :? string -> v :> obj
    | _ -> 
            let s = sprintf "Error unknown type %A" t
            raise (ApplicationException(s))

Answer 1

无需重新发明轮子，使用Convert.ChangeType .

如果您愿意，可以围绕它编写一个包装器，让编译器自动确定类型。

let inline getValue<'a> (s:string) = // limit to string only if desired
  System.Convert.ChangeType(s, typeof<'a>) :?> 'a

let x = getValue "1" + 1.2   // no need to explicitly state "float" anywhere here
printfn "%A" x                    // 2.2