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    <p>This rule can indeed be noisy, but there are some very valid reasons to avoid <code>List&lt;T&gt;</code> in library code. It all depends on the context. Here are a few things to consider before disabling the rule or suppressing a given occurrence:</p> <ul> <li><p><code>List&lt;T&gt;</code> is often a poor choice for input parameters as it forces callers to copy data unnecessarily. I have seen lots of code that declares parameters as <code>List&lt;T&gt;</code> or <code>T[]</code> when <code>IEnumerable&lt;T&gt;</code> would suffice.</p></li> <li><p><code>List&lt;T&gt;</code> can be a poor choice for properties as well. Consider the following alternatives:</p> <pre><code>public class Course { public List&lt;Course&gt; Prerequisites { get; } } public class Course { public Collection&lt;Course&gt; Prerequisites { get; } } </code></pre> <p>The intention is that the caller can change a course's prerequistes by modifying the collection. In that case, if we use <code>List&lt;Course&gt;</code>, there is no way for the <code>Course</code> class to be notified when the prerequisites change since <code>List&lt;T&gt;</code> does not provide any modification callbacks. As such, using <code>List&lt;T&gt;</code> in this context is like having arbitrarily many public fields. On the other hand, we can subclass <code>Collection&lt;T&gt;</code> and override its virtuals to be notified of changes.</p></li> </ul> <p><code>List&lt;T&gt;</code> works best as a return value when complete ownership of the collection is transferred to the caller. This is why <code>Enumerable.ToList()</code> is actually perfectly reasonable and it does not violate the spirit of the rule.</p> <p>Now that I think about it, allowing <code>List&lt;T&gt;</code> as a return value from methods, but continuing to flag <code>List&lt;T&gt;</code> properties and parameters would probably greatly improve the rule's signal to noise ratio...</p>
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    1. POVisual Studio Code Analysis Rule - "Do not expose generic lists"
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    1. USNick Guerrera
    1. USNick Guerrera
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    1. COIf `Course` simply wants to be notified when its prerequisites change, then `BindingList<Course>` would be a good option. It has events you can subscribe to, instead of having to derive a new class as with `Collection<Course>`
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      1. USBen Voigt
    2. CO@Ben Voigt Indeed. There is also `ObservableCollection<T>`. My point was not that `Collection<Course>` is necessarily the best choice, just that `List<Course>` is a poor choice in this context.
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