Scala 如何为地图编写 get(name:String, type:Class) [英] Scala How to write a get(name:String, type:Class) for map

问题描述

我希望能够有一个 [String,Any] 类型的地图实现，我可以在其中存储不同类的对象，然后我希望能够做到

I want to be able to have a map implementation of type [String,Any] in which i can store objects of different classes then i want to be able to do

import app.User;
....
usr = map.getAs("user",User)// with usr being an object of Class/Object User. If user is not of that type it throws an exception.

用户之前在地图中的存储位置.

where user was previously stored in the map.

这可能吗?

我什至可以是一个独立的方法，例如

I can even be a standalone method e.g

 usr = getAs(map,"user",User)

谢谢

推荐答案

您可以使用 ClassTag.我对此没有太多经验，但应该可以:

You can use ClassTag. I don't have a lot of experience with it, but something like that should work:

def getAs[T: ClassTag](m: Map[String, Any], key: String): T = 
  m(key).asInstanceOf[T]

用法:

val map = Map[String, Any]("one" -> 1, "hello"-> "world")
getAs[String](map, "hello")
res1: String = world

我让您处理异常，您可以简单地将 asInstanceOf 包装在 Try 中，或者您喜欢的任何策略.我还建议将返回类型更改为 Option[T].

I let you deal with the exception, you can simply wrap the asInstanceOf in a Try, or whichever strategy you prefer. I also recommend changing the return type to Option[T].

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