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POHow to make generic class that contains a Set of only its own type or subtypes as Children?
 

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  1. POHow to make generic class that contains a Set of only its own type or subtypes as Children?
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    <pre><code>abstract class Animal { } class Mammal : Animal { } class Dog : Mammal { } class Reptile : Animal { } class AnimalWrapper&lt;T&gt; where T : Animal { public ISet&lt;AnimalWrapper&lt;T&gt;&gt; Children { get; set; } } class Program { public static void Main(string[] args) { var foo = new AnimalWrapper&lt;Mammal&gt;(); foo.Children = new HashSet&lt;AnimalWrapper&lt;Mammal&gt;&gt;(); var child = new AnimalWrapper&lt;Dog&gt;(); foo.Children.Add(child); } } </code></pre> <p>This obviously doesn't compile because of <code>foo.Children.Add(child);</code></p> <p>I'm not sure if the above code is the most <em>clear</em> way to demonstrate what I want to do, so I will try to explain in plain English:</p> <p>I want the ability to have a class whose Children objects are in an <code>ISet</code> of the same generic type. Thus, if I also had <code>var child = new AnimalWrapper&lt;Reptile&gt;();</code> it would, at compile time, fail to do <code>foo.Children.Add(child);</code> because <code>Reptile</code> is not and does not inherit from <code>Mammal</code>. However, obviously, even if it's derived, as shown above, it doesn't work.</p> <p>Ultimately, it'd be nice to be able to say <code>ISet&lt;AnimalWrapper&lt;Animal&gt;&gt; baz = new HashSet&lt;AnimalWrapper&lt;Animal&gt;&gt;();</code> then add a <code>new AnimalWrapper&lt;Mammal&gt;()</code> to that set, and <code>new AnimalWrapper&lt;Reptile&gt;()</code> to the same set. And their children would have a property <code>Children</code> that's an <code>ISet&lt;AnimalWrapper&lt;T&gt;&gt;</code> where it's of its own type, in a way, as described above.</p> <p>Is there any way or am I just expecting too much from C#? Heck I'm confusing myself. :)</p> <p><strong>Edit:</strong> Ok, so I almost figured this out, without <code>AnimalWrapper</code>, but with a base <code>IAnimal</code> interface, it could almost work:</p> <pre><code>interface IAnimal { } abstract class Animal&lt;T&gt; : IAnimal where T : Animal&lt;T&gt; { public ISet&lt;T&gt; Children { get; set; } } class Mammal : Animal&lt;Mammal&gt; { } class Dog : Mammal { } class Reptile : Animal&lt;Reptile&gt; { } class Frog : Reptile { } class Program { public static void Main(string[] args) { var animals = new HashSet&lt;IAnimal&gt;(); // any animal can be in this var mammal = new Mammal(); animals.Add(mammal); mammal.Children = new HashSet&lt;Mammal&gt;(); var dog = new Dog(); mammal.Children.Add(dog); // ok! a dog is a mammal dog.Children = new HashSet&lt;Dog&gt;(); // in theory, OK, but compile time error // because Dog : Mammal, and Mammal defines Animal&lt;Mammal&gt;, therefore Dog's // Children is actually ISet&lt;Mammal&gt;, rather than ISet&lt;Dog&gt; (which is what // I want, recursively apply the T in Animal. Mammal mammal2 = new Mammal(); dog.Children.Add(mammal2); // should be verboten, but is allowed for the // same reason above. } } </code></pre>
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    1. CODid you try casting child as 'ATypeImpl'?
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      1. POHow to make generic class that contains a Set of only its own type or subtypes as Children?
      1. USDaniel Wardin
    2. COHow do you want to interact with the data structure once it's constructed?
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    3. COI think it would be easier to understand - and quite possibly to see where it would fall down - if you used more concrete names. But I'll try to have a look later on...
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      1. POHow to make generic class that contains a Set of only its own type or subtypes as Children?
      1. USJon Skeet
 

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