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PO.NET unique object identifier
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  1. PO.NET unique object identifier
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    copied!<p>Is there a way of getting a unique identifier of an instance?</p> <p><code>GetHashCode()</code> is the same for the two references pointing to the same instance. However, two different instances can (quite easily) get the same hash code:</p> <pre><code>Hashtable hashCodesSeen = new Hashtable(); LinkedList&lt;object&gt; l = new LinkedList&lt;object&gt;(); int n = 0; while (true) { object o = new object(); // Remember objects so that they don't get collected. // This does not make any difference though :( l.AddFirst(o); int hashCode = o.GetHashCode(); n++; if (hashCodesSeen.ContainsKey(hashCode)) { // Same hashCode seen twice for DIFFERENT objects (n is as low as 5322). Console.WriteLine("Hashcode seen twice: " + n + " (" + hashCode + ")"); break; } hashCodesSeen.Add(hashCode, null); } </code></pre> <p>I'm writing a debugging addin, and I need to get some kind of ID for a reference which is unique during the run of the program.</p> <p>I already managed to get internal ADDRESS of the instance, which is unique until the garbage collector (GC) compacts the heap (= moves the objects = changes the addresses).</p> <p>Stack&nbsp;Overflow question <em><a href="https://stackoverflow.com/questions/720177/default-implementation-for-object-gethashcode">Default implementation for Object.GetHashCode()</a></em> might be related.</p> <p>The objects are not under my control as I am accessing objects in a program being debugged using the debugger API. If I was in control of the objects, adding my own unique identifiers would be trivial.</p> <p>I wanted the unique ID for building a hashtable ID -> object, to be able to lookup already seen objects. For now I solved it like this:</p> <pre><code>Build a hashtable: 'hashCode' -&gt; (list of objects with hash code == 'hashCode') Find if object seen(o) { candidates = hashtable[o.GetHashCode()] // Objects with the same hashCode. If no candidates, the object is new If some candidates, compare their addresses to o.Address If no address is equal (the hash code was just a coincidence) -&gt; o is new If some address equal, o already seen } </code></pre>
 

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