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    <p>In this situation:</p> <pre><code>// We have an interface... interface InterfaceB {} // And this class implements the interface. class ImplementsB : InterfaceB {} // But this class does not. class DoesNotImplementB {} </code></pre> <p>You could define <code>MethodA</code> as:</p> <pre><code>static Type MethodA&lt;TClass, TInterface&gt;() where TClass : TInterface { return typeof(TClass); } </code></pre> <p>Then the following will work:</p> <pre><code>Type t = MethodA&lt;ImplementsB, InterfaceB&gt;(); </code></pre> <p>But this gives a compile-time error:</p> <pre><code>Type t = MethodA&lt;DoesNotImplementB, InterfaceB&gt;(); </code></pre> <blockquote> <p>The type 'DoesNotImplementB' cannot be used as type parameter 'TClass' in the generic type or method 'MethodA&lt;TClass,TInterface&gt;()'. There is no implicit reference conversion from 'DoesNotImplementB' to 'InterfaceB'.</p> </blockquote> <p>So, this way you are sure that the result of <code>MethodA</code> is a <code>Type</code> of a class that implements <code>TInterface</code>. Given that <code>Type</code> object, you can instantate it later like this:</p> <pre><code>public object Instantiate(Type type) { // Call the default constructor. // You can change this to call any constructor you want. var constructor = type.GetConstructor(Type.EmptyTypes); var instance = constructor.Invoke(new object[0]); return instance; } </code></pre> <p>If you know that your <code>Type</code> is compatible with some interface <code>TInterface</code>, then you can avoid a cast with an additional method like this:</p> <pre><code>public TInterface Instantiate&lt;TInterface&gt;(Type type) { return (TInterface)Instantiate(type); } </code></pre> <p>However, if <code>type</code> is a <code>Type</code> that somehow does not implement <code>TInterface</code>, you'll get an <code>InvalidCastException</code> at run-time. There is no way to constrain <code>Type</code> to be a type that implements a particular interface at compile-time. However, at run-time you can check it to avoid the <code>InvalidCastException</code> exception:</p> <pre><code>public TInterface Instantiate&lt;TInterface&gt;(Type type) { if (!typeof(TInterface).IsAssignableFrom(type)) throw new Exception("Wrong type!"); return (TInterface)Instantiate(type); } </code></pre> <p>Note that <code>typeof(TType)</code> is an expression that results in a <code>Type</code> object, so everywhere you see <code>typeof()</code> you could replace it with any <code>Type</code> variable and vice versa.</p> <p>Is this what you wanted to know?</p>
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    1. POHow to create a generic interface of a method that returns a Type of a class that implements an interface?
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    1. POHow to create a generic interface of a method that returns a Type of a class that implements an interface?
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    1. COClose, but I'm trying to avoid actually instantiating the object at this point. I want to return the class definition itself, of which I can use to instantiate the object later. My problem is I can't figure out a way to guarantee the (System.Type) returned, when instantiated, actually implements TInterface. At least, not until I try to instantiate it and cast it to TInterface. But that's a run-time solution, not a compile-time solution.
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    2. COI updated my post. Is this closer to what you wanted to know?
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    3. COI haven't forgotten about this, I just haven't had time to apply your ideas. They sound good, maybe I'll get a chance to try them out this weekend, and update this comment block about it when I can.
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