Is there a class like a Dictionary without a Value template? Is HashSet<T> the correct answer?
<p>I have 3 tables: Foos, Bars and FooBarConfirmations</p>

<p>I want to have a in-memory list of FooBarConfirmations by their hash:</p>

<pre><code>FooID   BarID   Hash
1       1       1_1
2       1       2_1
1       2       1_2
2       2       2_2
</code></pre>

<p>What would be the best Class to use to store this type of structure in-memory, so that I can quickly check to see if a combination exists like so:</p>

<pre><code>list.Contains("1_2");
</code></pre>

<p>I can do this with Dictionary&lt;string,anything&gt;, but it "feels" wrong.</p>

<p>HashSet looks like the right tool for the job, but does it use some form of hashing algorithm in the background to do the lookups efficiently?</p>
