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POHow well does .NET dictionary resolve collisions?
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copied!<p>I have a problem with a custom object that needs to be keyed for a table. I need to generate a unique numeric key. I'm having collision problems and I'm wondering if I can leverage a dictionary to help me. Assume I have an object like this:</p> <pre><code>class Thingy { public string Foo; public string Bar; public string Others; } </code></pre> <p>and so on with more fields. Lets say Foo and Bar are my key fields - if they're equal between two Thingys, then the two objects should be considered equal (one may represent an update to the other, with Others fields being updated.) So I have these:</p> <pre><code>public override bool Equals(object obj) { Thingy thing = (Thingy)obj; // yes I do type check first return (this.Foo == thing.Foo && this.Bar == thing.Bar); } public override int GetHashCode() { return (this.Foo + this.Bar).GetHashCode(); // using default string impl } </code></pre> <p>so this works for the most part, but there are rare occasions where two Thingys that are actually different have the same hash code.</p> <p>My question is this: could I use a Dictionary<code><Thingy, int</code>> where I put in my Thingys, and use a sequential value coming out of the dictionary as my actual key? I'm wondering if the Dictionary, when detecting a rare hash code collision, will call my Equals method, determine that the objects are actually different, and store them differently. I imaging then when looking it up, it would see a bucket for that hash and search for the correct Thingy, again using Equals for comparison.</p> <p>Is this the case with dictionary, or does it only resolve collisions where the hash code is different, but (hash % size) is the same? If this won't work, what might?</p>

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