如何知道对象是否是 TypeTag 类型的实例? [英] How to know if an object is an instance of a TypeTag's type?

问题描述

我有一个函数可以知道一个对象是否是Manifest 类型的一个实例.我想将其迁移到 TypeTag 版本.旧函数如下:

I have a function which is able to know if an object is an instance of a Manifest's type. I would like to migrate it to a TypeTag version. The old function is the following one:

def myIsInstanceOf[T: Manifest](that: Any) = 
  implicitly[Manifest[T]].erasure.isInstance(that)

我一直在试验 TypeTag，现在我有了这个 TypeTag 版本:

I have been experimenting with the TypeTags and now I have this TypeTag version:

// Involved definitions
def myInstanceToTpe[T: TypeTag](x: T) = typeOf[T]
def myIsInstanceOf[T: TypeTag, U: TypeTag](tag: TypeTag[T], that: U) = 
  myInstanceToTpe(that) stat_<:< tag.tpe

// Some invocation examples
class A
class B extends A
class C

myIsInstanceOf(typeTag[A], new A)        /* true */
myIsInstanceOf(typeTag[A], new B)        /* true */
myIsInstanceOf(typeTag[A], new C)        /* false */

有没有更好的方法来完成这个任务?是否可以省略参数化的 U，使用 Any 代替(就像在旧函数中所做的那样)?

Is there any better way to achieve this task? Can the parameterized U be omitted, using an Any instead (just as it is done in the old function)?

推荐答案

如果对已擦除的类型使用子类型检查就足够了，请按照 Travis Brown 在上面评论中的建议进行操作:

If it suffices to use subtyping checks on erased types, do as Travis Brown suggested in the comment above:

def myIsInstanceOf[T: ClassTag](that: Any) =
  classTag[T].runtimeClass.isInstance(that)

否则你需要明确地拼出 U 类型，以便 scalac 在一个类型标签中捕获它的类型:

Otherwise you need to explicitly spell out the U type, so that scalac captures its type in a type tag:

def myIsInstanceOf[T: TypeTag, U: TypeTag] =
  typeOf[U] <:< typeOf[T]

这篇关于如何知道对象是否是 TypeTag 类型的实例?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！