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POWhy doesn't generic ICollection implement IReadOnlyCollection in .NET 4.5?
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  1. POWhy doesn't generic ICollection implement IReadOnlyCollection in .NET 4.5?
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    copied!<p>In .NET 4.5 / C# 5, <code>IReadOnlyCollection&lt;T&gt;</code> is declared with a <code>Count</code> property:</p> <pre><code>public interface IReadOnlyCollection&lt;out T&gt; : IEnumerable&lt;T&gt;, IEnumerable { int Count { get; } } </code></pre> <p>I am wondering, wouldn't it have made sense for <code>ICollection&lt;T&gt;</code> to implement the <code>IReadOnlyCollection&lt;T&gt;</code> interface as well:</p> <pre><code>public interface ICollection&lt;T&gt; : IEnumerable&lt;T&gt;, IEnumerable, *IReadOnlyCollection&lt;T&gt;* </code></pre> <p>This would've meant that classes implementing <code>ICollection&lt;T&gt;</code> would've automatically implemented <code>IReadOnlyCollection&lt;T&gt;</code>. This sounds reasonable to me.</p> <p>The <code>ICollection&lt;T&gt;</code> abstraction can be viewed as an extension of the <code>IReadOnlyCollection&lt;T&gt;</code> abstraction. Note that <code>List&lt;T&gt;</code>, for example, implements both <code>ICollection&lt;T&gt;</code> and <code>IReadOnlyCollection&lt;T&gt;</code>.</p> <p>However it has not been designed that way. </p> <p>What am I missing here? Why would the current implementation have been chosen instead?</p> <hr> <p><strong>UPDATE</strong></p> <p>I'm looking for an answer that uses <strong>Object Oriented design reasoning</strong> to explain why:</p> <ul> <li>A concrete class such as <code>List&lt;T&gt;</code> implementing both <code>IReadOnlyCollection&lt;T&gt;</code> <em>and</em> <code>ICollection&lt;T&gt;</code></li> </ul> <p><em>is a better design than:</em></p> <ul> <li><code>ICollection&lt;T&gt;</code> implementing <code>IReadOnlyCollection&lt;T&gt;</code> directly</li> </ul> <hr> <p>Also please note that this is essentially the same question as:</p> <ol> <li>Why doesn't <code>IList&lt;T&gt;</code> implement <code>IReadOnlyList&lt;T&gt;</code>?</li> <li>Why doesn't <code>IDictionary&lt;T&gt;</code> implement <code>IReadOnlyDictionary&lt;T&gt;</code>?</li> </ol>
 

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