Pattern match on class literals

David P posted one way:

> Date: Wed, 7 Jan 2009 12:42:16 -0800
> From: David Pollak
> CC:
>
> scala> val StrCls = classOf[String]
> StrCls: java.lang.Class[String] = class java.lang.String
>
> scala> val ObjCls = classOf[Object]
> ObjCls: java.lang.Class[java.lang.Object] = class java.lang.Object
>
> scala> def m(c: Class[_]) = c match {
> | case ObjCls => "Object"
> | case StrCls => "String"
> | case _ => "Huh?"
> | }
> m: (Class[_])java.lang.String
>
> scala> m(classOf[String])
> res1: java.lang.String = String
>
> scala> m(classOf[AnyRef])
> res2: java.lang.String = Object
>
> scala> m(classOf[Int])
> res3: java.lang.String = Huh?

although you stated

> > I need to match on a bunch of possibilities, so defining uppercase
> > constants for each one isn't such a good idea

But perhaps there is an alternative way to achieve what you want.

Can you instead match on an instance (i.e. you did not state where clazz
is coming from... If it is

val clazz = o.getClass()

then instead you may want to just use:

o match {
case i : String => ...
case m : MyType => ...
case y : YourType => ...
}

Or, perhaps you can use a classMap : Map[Class,Runnable] = {...} and then simply call

classMap(clazz).run()

scala> val StrCls = classOf[String]
StrCls: java.lang.Class[String] = class java.lang.String

scala> val ObjCls = classOf[Object]
ObjCls: java.lang.Class[java.lang.Object] = class java.lang.Object

scala> def m(c: Class[_]) = c match {
     | case ObjCls => "Object"      
     | case StrCls => "String"      
     | case _ => "Huh?"             
     | }
m: (Class[_])java.lang.String

scala> m(classOf[String])
res1: java.lang.String = String

scala> m(classOf[AnyRef])
res2: java.lang.String = Object

scala> m(classOf[Int])  
res3: java.lang.String = Huh?


On Wed, Jan 7, 2009 at 12:35 PM, Naftoli Gugenheim <naftoligug [at] gmail [dot] com> wrote:

How do you pattern match on something like class literals, or for that matter anything that is only available from a function that starts with lowercase? clazz match {  case classOf[java.lang.Integer] => ... } doesn't work, and adding back ticks `...` causes the [ to be invalid syntax. I need to match on a bunch of possibilities, so defining uppercase constants for each one isn't such a good idea, and putting the comparison as an if guard:   case c if c==classOf[...] => ... seems to make pattern matching extra -- I might as well just right a bunch of if/else ifs, which is what I did in meanwhile. Another option that I don't like is matching on clazz.getName Similar situations (not tested recently):  case v.getA =>  case getCalculation(param) => Is there no straightforward solution for such a typical scenario? Thanks!  

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