InstanceOf some type from runtime, Scala

Question

The idea, is that, for example we got type of some object:

val tm = getTypeTag("String here").tpe
//> tm: reflect.runtime.universe.Type = java.lang.String

// for example I got another val or var, of some type:

val tmA: Any = "String here"
//> tmA: Any = String here

How to make tmA.InstanceOf(tm) (it is a mnemonic code)? 'Cause tm it is not a type alias, and we cant make InstanceOf[tm] exactly.

EDITED

there I mean analog function for asIstanceOf, to make a sort of type casting

EDITED2

I'll partly answer my question myself. So if we have TypeTags is is all easy!

def tGet[T](t: TypeTag[T], obj: Any): T = obj.asInstanceOf[T]

It is a harder situation if we only got Type and not the whole TypeTag[T].

Travis Brown · Accepted Answer · 2013-11-18 10:52:14Z

6

You can use a mirror to reflect the instance:

val mirror = runtimeMirror(getClass.getClassLoader)

def isTm(a: Any) = mirror.reflect(a).symbol == tm.typeSymbol

And then:

scala> isTm("String here": Any)
res0: Boolean = true

scala> isTm(List("String here"): Any)
res1: Boolean = false

I don't think I have to tell you what a bad idea this is, though.

answered Nov 18, 2013 at 10:52

Travis Brown

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3 Comments

DaunnC Over a year ago

thx for reply! that's right, and is not a good idea. but the idea, is that I have 100% sure, that the object is of that type. Mb I have a sort of mistake in my question, but I meant .asInstanceOf(tm) so to make a sort of casting.. so for example tm is ru.Type = String, and function myAsInstanceOf(tm) is in fact the same as asInstanceOf[String]

Travis Brown Over a year ago

Oh, I did misunderstand then—I read InstanceOf as meaning isInstanceOf. I think you'll need a type tag (or macro) for the cast—I'll try to put together an answer when I get a chance.

DaunnC Over a year ago

thx! that would be great... And I'll try to avoid this, and post here, if it would be possible of cource.

Soroosh Sarabadani · Accepted Answer · 2013-11-19 06:16:28Z

-1

You need just to use type attribute of your variable after the variable. As an example you can write:

val h ="hello" val b:Any = "hhhh"

val stringB: String = b.asInstanceOf[h.type]

println(stringB)

answered Nov 19, 2013 at 6:16

Soroosh Sarabadani

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1 Comment

Travis Brown Over a year ago

But he's trying to cast to the type represented by a Type value (or a TypeTag value), not to the type of some given value.

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