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Compare static TypeTag to runtime Class
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import scala.reflect.runtime.universe._ | |
class A[E](e:E)(implicit t: TypeTag[E]){ | |
def c(o:Any) = { | |
val TypeRef(_, klass_symbol, _) = t.tpe | |
println(s"ClassSymbol extracted from TypeTag[E] '${klass_symbol.asClass}' : ClassSymbol") | |
println(s"Class extracted from o:Any parameter = '${o.getClass}' : Class[??]") | |
runtimeMirror(getClass.getClassLoader).runtimeClass(klass_symbol.asClass) == o.getClass | |
} | |
} | |
(new A(1)) c 2 // fails! Int and java.lang.Integer | |
(new A("a") "b") // succeeds! | |
/* -- My understanding -- | |
difference between types and classes: | |
they are closely related BUT: | |
Multiple classes (accessible through different class loaders) can implement the same Type. | |
A "Type" is a set of valid objects, possibly defined by some constraints. | |
A "Class" (defined through the help of type annotations) is AN implementation of a Type, | |
but different classes (accessible through different classloaders in the JVM world) can implement | |
different behaviours. Thus we can have different classes matching the same type. | |
Why doesn't this work then: | |
class A {} | |
class B {} | |
typeOf[A] =:= typeOf[B] // <- false | |
Well it seems that the name of the class is an element of it's type (at least for JVM/Scala). | |
*/ | |
// nice thing i can do now | |
class CompareThing[E : TypeTag](val o : E) { | |
def test(that : E) : Boolean = { | |
println("yay!") // just something, anything | |
true | |
} | |
override def equals(that: Any): Boolean = { | |
def klass(s: Symbol) = runtimeMirror(getClass.getClassLoader).runtimeClass(s.asClass) | |
typeOf[E] match { | |
case TypeRef(_, symbol, _) if klass(symbol) == that.getClass => test(that.asInstanceOf[E]) | |
case _ => false | |
} | |
} | |
} | |
(new CompareThing("a")) == 2 // returns false | |
(new CompareThing("a")) == "b" // returns true! |
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