在Elm中初始化一个空文件值 | 在Elm中初始化一个空文件值

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问题描述

我正在使用Elm（0.18），并导入了simonh1000的库。要存储文件值，我们使用以下类型：

I am using Elm (0.18) and imported simonh1000's FileReader library. To store a file value, we use the following type:

import Json.Decode as Json exposing (Decoder, Value)
...
{-| An ArrayBuffer is a Elm Json Value.
-}
type alias FileContentArrayBuffer =
    Value

我想要用一个空的占位符初始化我的模型。我这样做如下：

I want to initialize my model with an empty placeholder. I do this as follows:

type alias Model =
  {
     username : String
   , filecontent: FileContentArrayBuffer
  }

initialModel : Model
initialModel =
  {
     username = "mark"
   , filecontent = Nothing
  }

但是编译器给我这个错误：

But the compiler gives me this error:

The type annotation for `initialModel` says it is a:

    Model

But the definition (shown above) is a:

    { username : String
    , filecontent : Maybe a
    }

推荐答案

由于是 Json.Encode.Value ，如果您真的要初始化ea Value 类型作为JSON {} ，您可以执行以下操作：

Since Json.Decode.Value is an alias for Json.Encode.Value, if you really want to initialize a Value type as a JSON {}, you can do the following:

filecontent = Json.Encode.object []

但是，我认为在您的情况下，重构为也许是FileContentArrayBuffer 字段类型更有意义，因为，您如何处理 Value 类型会解码为 {} 吗？ 没什么的值显然更合适和习惯。

However, I think in your case, it makes more sense to refactor to a Maybe FileContentArrayBuffer field type, since, what would you do with an Value type that decodes to {} anyway? A Nothing value definitely seems more fitting and idiomatic.

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