C# existential type
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using System;
class MagicBox{
private Object member;
private Type type;
public static MagicBox createMagicBox<T>(T obj){
MagicBox box=new MagicBox();
box.member=obj;
box.type=typeof(T);
return box;
}
public T unwrap<T>(){
return (T)member;
}
public bool is_a<T>(){
Type t=typeof(T);
return type==t;
}
}
class MainClass {
static void Main() {
Console.WriteLine("Hello World!");
MagicBox box=MagicBox.createMagicBox(20);
if(box.is_a<int>()){
Console.WriteLine("Yes. "+box.unwrap<int>());
}else{
Console.WriteLine("Nope.");
}
if(box.is_a<float>()){
Console.WriteLine("Yes.");
}else{
Console.WriteLine("Nope.");
}
}
}
Csharp
INFO