向上转换通过反射创建的 F# 记录

Question

我一直在搞乱 F# 和它的反射，试图从 F# 中动态创建一个 Record 类型对象，我让它的大部分工作正常（如下所示），但有一件事 - 我通过反射创建的记录具有类型“ obj”而不是它应该的（“人”），我似乎无法以任何方式升级它。

#light

type Person = {
    Name:string;
    Age:int;
}

let example = {Name = "Fredrik"; Age = 23;}
// example has type Person = {Name = "Fredrik"; Age = 23;}

let creator = Reflection.FSharpValue.PrecomputeRecordConstructor(example.GetType(), 
               System.Reflection.BindingFlags.Public)

let reflected = creator [| ("thr" :> obj); (23 :> obj) |]
// here reflected will have the type obj = {Name = "thr"; Age = 23;}

// Function that changes the name of a Person record
let changeName (x:Person) (name:string) = 
    { x with Name = name }

// Works with "example" which is has type "Person"
changeName example "Johan"

// But not with "reflected" since it has type "obj"
changeName reflected "Jack" // Error "This expression has type obj but is here used with type Person. "

// But casting reflected to Person doesn't work either
(reflected :> Person) // Type constraint mismatch. The type   obj is not compatible with 
                      // type  Person. The type 'obj' is not compatible with the type 'Person'. 
                      // C:\Users\thr\Documents\Visual Studio 2008\Projects\
                      // Reflection\Reflection\Script.fsx   34  2   Reflection

Answer 1

尝试使用其他强制转换运算符（因为这次您以另一种方式强制转换）

所以changeName（反映:?> Person）“Jack”