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POInterfaces inheritance in C#
 

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    <p>I'm trying to overrun quite big (for me) problem that I came across while writing my application. Look at this, please (I will try to shorten the code for simplicity):</p> <p>I have root interface called <code>IRepository&lt;T&gt;</code>. Next, <code>IBookRepository : IRepository&lt;Book&gt;</code> Next, concrete class that implements it: <code>BookRepository : IBookRepository</code></p> <p>In the RepositoryManager class I declared <code>private IRepository&lt;IRepoItem&gt; currentRepo;</code></p> <p><code>IRepoItem</code> is an interface that is implemented by Book class.</p> <p>Now, when I try to do something like this:</p> <pre><code>currentRepo = new BookRepository(); </code></pre> <p>VisualStudio gives error message:</p> <blockquote> <p><strong>Cannot implicitly convert type 'BookRepository' to 'IRepository'. An explicit conversion exists (are you missing a cast?)</strong></p> </blockquote> <p>I tried to cast explicitly, but runtime exception is thrown...</p> <p>I know (almost for sure) that it is something called covariance and this is (probably) solved in .Net 4.0. Unfortunately I'm writing using framework version 3.5, and I cannot change this. Please give me some advices what to do - how to overrun this problem? I'd like to get currentRepo from RepoFactory that would produce few kinds of repositories depends on user needs. I don't know whether links are allowed here, but I write some kind of blog on <a href="http://olgatherer.wordpress.com/" rel="nofollow">http://olgatherer.wordpress.com/</a> where I describe application creation. My English isn't good, but I hope that it's enough to understand me. Thank you in advance for answer.</p> <p>Best regards, skrzeczowas</p>
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    1. USWill Marcouiller
    1. USskrzeczowas
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    1. COWhat is the declared type of currentRepo?
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      1. USJohn Bledsoe
    2. CONever mind, I see it is an IRepository<IRepoItem>.
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      1. USJohn Bledsoe
 

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