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    <p>It is considered good practice to work with the highest possible class in the hierarchy. So if you only need to loop through the values you should only expose <code>IEnumerable&lt;T&gt;</code>:</p> <pre><code>IEnumerable&lt;Facility&gt; Facilities = new List&lt;Facility&gt;(); // now you can foreach over the facilities or chain with LINQ </code></pre> <p>If you need indexer access you could use <code>IList&lt;Facility&gt;</code></p> <pre><code>IList&lt;Facility&gt; Facilities = new List&lt;Facility&gt;(); // in addition to looping now you can access facilities by index // and you can also add and remove facilities </code></pre> <p>The idea behind exposing the highest possible class/interface in the hierarchy when designing some API is that this way you are hiding the implementation details that you are using a <code>List&lt;T&gt;</code>. If you tomorrow you invent a <code>HyperSpecialListWhichIsVeryFast&lt;T&gt;</code> which implements the contract that you agreed upon with the consumer of the API, this consumer doesn't need to change anything in his code. He doesn't care. He works with <code>IEnumerable&lt;T&gt;</code> because all he needs is to loop for example. And thanks to your new list his code will run faster without him needing to change anything.</p> <p>But using a non-generic à la .NET 1.0 weakly typed collections which are in the history books now is like voodoo magic:</p> <pre><code>IList Facilities = new List&lt;Facility&gt;(); </code></pre> <p>Cannot think of any reason why this would be useful. Downcasting to a non-generic version will force the client to cast in order to access the underlying type <code>T</code>. This way he is loosing all the compile-time safety that generics provide.</p>
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    1. USDarin Dimitrov
    1. USDarin Dimitrov
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    1. COThe weird thing there is that they are downcasting to IList and not IList<Facility>();
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      1. USivowiblo
    2. COagreed! I would also always use the templated version and not the generic one!
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      1. USMario The Spoon
    3. CO@ivowiblo, yes, that's the weird thing. Can't think of a good reason why one would do this.
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