Scala 中泛型类型的模式匹配 [英] Pattern matching on generic type in Scala

问题描述

我有如下所示的 Scala 函数:

I have scala function that looks like this:

现在，取决于 T 的类型(在我的例子中，它可以是 Double、Boolean 和 LocalDate)，我需要在 ob 上应用函数.像这样的东西(我知道代码没有意义，但我试图传达我的意思):

Now, depending upon the type of T (In my case, it can be Double, Boolean and LocalDate), I need to apply functions on ob. Something like this (I know the code will make no sense but I am trying to convey what I mean to do):

def X[T](ob: Observable[T]): Observable[T] = {
    //code  
    T match {
    case Double => DoSomething1(ob:Observable[Double]):Observable[Double]
    case Boolean => DoSomething2(ob:Observable[Boolean]):Observable[Boolean]
    case LocalDate => DoSomething3(ob:Observable[LocalDate]):Observable[LocalDate]
    }
}

考虑到 Scala 的 Erasure 属性，可以以某种方式使用反射来完成工作吗?甚至有可能吗?

Taking into consideration the Erasure property of Scala, can reflection be somehow used to get the job done? Is it even possible?

推荐答案

如果你使用的是 2.10+，我会选择 TypeTag

I would go with TypeTag if you're on 2.10+

import reflect.runtime.universe._

class Observable[Foo]

def X[T: TypeTag](ob: Observable[T]) = ob match {
    case x if typeOf[T] <:< typeOf[Double]   => println("Double obs")
    case x if typeOf[T] <:< typeOf[Boolean]  => println("Boolean obs")
    case x if typeOf[T] <:< typeOf[Int]      => println("Int obs")
}

X(new Observable[Int])
// Int obs

另见这个冗长但很棒的答案

另请注意，我只是瞥了一眼 Scala 反射，所以可能有人会写出一个更好的 TypeTag 用法示例.

Note also that I only took a glimpse at scala reflection, so likely somebody may write a better example of TypeTag usage.

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