F# 代碼不夠通用（使用靜態成員約束）

Question

我正在嘗試創建一個通用函數，用於檢查記錄是否采用有效格式，前提是記錄實現了靜態成員有效。 當嘗試在 Bolero (Blazor) 框架內的 ElmishComponent 中使用它時，我收到以下錯誤

此代碼不夠通用。 類型變量 ^childModel 當 ^childModel : (static member valid : ^childModel -> bool) 無法泛化，因為它會超出其范圍

使用以下代碼

module Modal =
    type Message<'childModel, 'childMessage> = | Confirm of 'childModel | Cancel | ChildMessage of 'childMessage
    type Model<'T> = { Display : bool; Title : string; Child : 'T }
    let inline valid (x: ^t) =
        (^t: (static member valid: ^t -> bool) (x))

    type Component<'T, ^childModel, 'childMessage when 'T :> ElmishComponent< ^childModel, 'childMessage> and ^childModel : (static member valid: ^childModel -> bool)>() =
        inherit ElmishComponent<Model<'childModel>, Message<'childModel, 'childMessage>>()

        // Error is highlighted on this line
        override this.View model dispatch = 
            cond model.Display <| function
            | true ->
                div [ attr.style (if model.Display then "background: lightblue;" else "background: grey;") ] [
                    h3 [] [ text model.Title ]
                    ecomp<'T,_,_> model.Child (dispatch << ChildMessage)
                    p [] []
                    button [ 
                        // This is where I use the valid function
                        attr.disabled (if valid model.Child then null else "true")
                        on.click (fun _ -> dispatch <| Confirm model.Child)
                    ] [ text "Confirm" ]
                    button [ on.click (fun _ -> dispatch Cancel) ] [ text "Cancel" ]
                ]
            | false ->
                empty

Answer 1

我可能遺漏了一些東西，但在我看來，一種更簡單的方法是使用子模型實現的接口 - 那么你根本不必理會靜態成員約束：

type IValidable =
  abstract IsValid : bool

type Component<'T, 'childModel, 'childMessage when 
      'T :> ElmishComponent< 'childModel, 'childMessage> and 
      'childModel :> IValidable>() =
    inherit ElmishComponent<Model<'childModel>, Message<'childModel, 'childMessage>>()
    override this.View model dispatch = 
        let test = model.Child.IsValid            
        ()