类型推断失败:没有足够的信息来推断参数，请明确指定 [英] Type inference failed: Not enough information to infer parameter Please specify it explicitly

问题描述

我正在尝试用Kotlin编写Vaadin应用程序.对于数据绑定，Vaadin 8现在提供了类型安全数据绑定的可能性.在Kotlin中，我期望这样的工作:

I'm trying to write a Vaadin application in Kotlin. For data binding, Vaadin 8 now provides a possibility for type safe data binding. In Kotlin I would have expected work like that:

class LoginModel {
    var username: String = ""
    var password: String = ""
}

class LoginView : FormLayout() {
  val name = TextField("name")
  val password = TextField("password")
  val loginButton = Button("login")

  init {
      val binder = Binder<LoginModel>()
      binder.forField(name).bind(
          { it.username }, 
          { bean, value -> bean.username = value })

     //... 
  }
}

我在这里收到以下错误消息:

I'm getting the following error message here:

Error:(23, 31) Kotlin: Type inference failed: Not enough information to infer parameter BEAN in fun <BEAN : Any!, TARGET : Any!, BEAN : Any!> Binder.BindingBuilder<BEAN#1 (type parameter of bind), TARGET>.bind(p0: ((BEAN#1!) -> TARGET!)!, p1: ((BEAN#1!, TARGET!) -> Unit)!): Binder.Binding<BEAN#1!, TARGET!>!
Please specify it explicitly.

我通过显式指定类型参数来尝试:

I tried by explicit specifying the type parameters:

binder.forField(name).bind<LoginView, String, LoginView>(
    { it.username }, 
    { bean, value -> bean.username = value })

但这会导致错误消息(以及其他语法错误，因此我没有遵循该方法)

but that leads to the error message (and other sytax errors, so I did not follow that approach)

Error:(23, 35) Kotlin: No type arguments expected for fun bind(p0: ValueProvider<LoginModel!, String!>!, p1: Setter<LoginModel!, String!>!): Binder.Binding<LoginModel!, String!>! defined in com.vaadin.data.Binder.BindingBuilder

我的第二种方法是尝试直接传递Kotlin属性访问器，但是错误消息与第一种相同:

My second approach was trying to pass the Kotlin property accessors directly, but the error message was the same as the first one:

binder.forField(name).bind(LoginModel::username.getter, LoginModel::username.setter)

最后一种方法是尝试使用扩展方法并使所有内容尽可能明确:

The last approeach was trying to use an extension method and make everything as explicit as possible:

fun <BEAN, TARGET> Binder.BindingBuilder<BEAN, TARGET>.bind(property: KMutableProperty1<BEAN, TARGET>) {

    fun set(bean: BEAN): TARGET = property.get(bean)
    fun get(bean: BEAN, value: TARGET): Unit = property.set(bean, value)
    this.bind(::set, ::get)
}

但是它仍然导致与第一个相同的错误消息

But it leads still to the same error message as the first one

推荐答案

我已经尝试了您的示例，并且使用我的Intellij 2017.1.4和Kotlin 1.1.2-5可以很好地进行编译.可能是您发现了较旧版本的Kotlin插件中的错误?

I have tried your example and it compiles just fine with my Intellij 2017.1.4 and Kotlin 1.1.2-5. Probably you have discovered a bug in older version of a Kotlin plugin?

方法bind不使用通用参数，因此无法泛化. forField方法采用一个通用参数，因此也许您可以尝试

The method bind takes no generic parameters so it cannot be generified. The forField method takes one generic parameter, so perhaps you can try

    binder.forField<String>(name).bind(
            { it.username },
            { bean, value -> bean.username = value })

但是首先，请确保您具有最新版本的Kotlin插件，和/或尝试使用Intellij Community Edition进行试用.

But first, please make sure that you have the newest version of the Kotlin plugin, and/or perhaps try it out with Intellij Community Edition.

但是，我建议您使用bind(String)，因为其他绑定方法不适用于JSR303验证.您还可以定义以下扩展方法:

However, I urge you to use bind(String) since other bind methods won't work with JSR303 validations. You can also define the following extension method:

fun <BEAN, FIELDVALUE> Binder.BindingBuilder<BEAN, FIELDVALUE>.bind(prop: KMutableProperty1<BEAN, FIELDVALUE?>): Binder.Binding<BEAN, FIELDVALUE> =
        bind(prop.name)

并从您的代码binder.forField(name).bind(LoginModel::username)中进行如下调用.请在此处查看更多示例:

And call it as follows from your code binder.forField(name).bind(LoginModel::username). Please see here for more examples: https://github.com/mvysny/karibu-dsl/blob/master/example-v8/src/main/kotlin/com/github/vok/karibudsl/example/form/FormView.kt

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