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POStrongly typed way of storing type references
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  1. POStrongly typed way of storing type references
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    copied!<p>I need to store a collection of types.</p> <p>All types implement the same interface <code>IHandler&lt;T&gt;</code>, where <code>T</code> is a parameter of the parent class.</p> <p>At runtime, I enumerate the list of handlers and process a message. Each handler is created by a builder (just uses StructureMap internally). The builder exposes a method like:</p> <pre><code>static void DoSomething&lt;T&gt;(Action&lt;T&gt; action) { } </code></pre> <p>Of course, I only have a <code>Type</code> so can't use the above.</p> <p>I've got round this by also passing the underlying interface as the generic parameter and the concrete type as a parameter:</p> <pre><code>DoSomething&lt;IHandler&lt;T&gt;&gt;(handlerType, h =&gt; { h.Handle(message); }); </code></pre> <p>Then inside <code>DoSomething</code> I can get an instance of <code>handlerType</code> but cast it as <code>IHandler&lt;T&gt;</code>.</p> <p>Just wondered if there was a better/cleaner way.</p> <h3>Update</h3> <p>In response to some of the comments.</p> <p>The collection is an <code>ICollection&lt;Type&gt;</code>, not instances. The message handlers are created on demand, on different threads, for each batch of messages, so creating the handlers in advance, or using <code>Lazy&lt;T&gt;</code>, was not an option.</p> <p>Essentially I am trying to abstract away some direct references to StructureMap. Specifically, <code>DoSomething&lt;T&gt;</code> actually creates the handler using a nested container, before executing the action (it's <code>Handle</code> method).</p> <h3>Update 2 (solution)</h3> <p>I realized that I could handle (no pun intended) this better by storing a collection of <code>Action&lt;T&gt;</code> and creating the handlers using a factory. Here's a simple example:</p> <pre><code>public class SimpleProcessor&lt;T&gt; where T : IMessage { ICollection&lt;Action&lt;T&gt;&gt; handlers; T message; public SimpleProcessor(T message) { this.handlers = new List&lt;Action&lt;T&gt;&gt;(); this.message = message; } public void AddHandler(Action&lt;T&gt; handler) { handlers.Add(handler); } public void Process() { foreach (var handler in handlers) { handler(message); } } } </code></pre> <p>Usage:</p> <pre><code>var testMessage = new TestMessage { Message = "Foo" }; var simpleProcessor = new SimpleProcessor&lt;TestMessage&gt;(testMessage); simpleProcessor.AddHandler(m =&gt; DoSomething&lt;TestMessageHandler&gt;(h =&gt; h.Handle(m))); simpleProcessor.Process(); </code></pre> <p>I'm more or less happy with this solution.</p>
 

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