Imagine a class, a simple object… Add a protected static property to it. Now imagine have multiple classes extending it, what role does the static property take on? It is shared, right — meaning that both sub-classes can interact with the shared property since it is static, there is only one.
If you’re familiar with C#, terms like inheritance and static are commonplace. Without querying your favorite search engine or pasting the code into your favorite C# IDE — do you know the answer to this questions?
Consider the following:
class Program
{
static void Main(string[] args)
{
var one = new ExtendsOne();
one.Put(Guid.Empty, new { OMG = "WTF" });
var value = one.Get(Guid.Empty);
Console.WriteLine(value);
var two = new ExtendsTwo();
two.Put(2, "Seriously, interesting...");
var @string = two.Get(2);
Console.WriteLine(@string);
Console.ReadKey();
}
abstract class Generic<TKey, TValue>
{
protected static readonly IDictionary<TKey, TValue>
Cache = new Dictionary<TKey, TValue>();
public abstract TValue Get(TKey key);
public abstract TValue Put(TKey key, TValue value);
}
sealed class ExtendsOne : Generic<Guid, object>
{
public override object Get(Guid key)
{
return Cache[key];
}
public override object Put(Guid key, object value)
{
return Cache[key] = value;
}
}
sealed class ExtendsTwo : Generic<int, string>
{
public override string Get(int key)
{
return Cache[key];
}
public override object Put(int key, string value)
{
return Cache[key] = value;
}
}
Does this compile?
Yes, it does — good you’re with me so far!
Does this throw a runtime exception?
No, it does not… What I found interesting is that the static property Cache is created anew for each subclass of a different type. Which actually makes perfect sense, but it kind of makes you rethink static a little.
It is almost like having an instance of a static which is not normally what you expect when you think of statics. Typically, one would expect it to be shared — but with the power of generics I guess anything is possible.
CSharper 