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copied!<p>You’re thinking way too complicated.</p> <blockquote> <p>Does the reference 'f' contain type information itself?</p> </blockquote> <p>No. It doesn’t have to. It is simply an address to the beginning of the <code>Bar</code> object’s memory that was constructed earlier. <em>That</em> object contains a virtual method table (and possibly a reference to its associated <code>Type</code> object<sup>1</sup>, but that’s irrelevant here).</p> <blockquote> <p>When I call f.Baz(), am I right in thinking that the dispatch occurs via Bar's MethodTable anyway?</p> </blockquote> <p>Yes.</p> <blockquote> <p>Is it simply that case that the C# compiler uses flow analysis to work out what's going on and prevent any illegal operations?</p> </blockquote> <p>Flow analysis is complex and completely unnecessary here. The compiler allows exactly those operations that are allowed for the declaration type of <code>f</code> – which is <code>Foo</code>. The compiler doesn’t <em>care</em> about the actual (= dynamic) type of <code>f</code> at all.</p> <blockquote> <p>could you tell what the original declaration was from the resultant IL?</p> </blockquote> <p>Depends. An <em>object</em> doesn’t <em>have</em> a static type so “telling its static type at runtime” is meaningless. Declarations, on the other hand, differ. If the variable is a formal parameter of a method then sure, you can (at runtime) use reflection to determine the declaration type of the method’s parameter.</p> <p>For local variables, once again this operation is meaningless. On the other hand, the IL <em>does</em> store this information (as metadata?) via <code>.locals</code> so the code <em>can</em> theoretically be reverse engineered (Cecil and Reflector do this) to get the static type of variables.</p> <hr> <p><sup>1</sup> I’m guessing here but this is actually <em>improbable</em>. If each object held its own reference to an associated <code>Type</code> object, that would mean an additional overhead of a pointer. Additionally, this reference is entirely unnecessary, since the object can simply call <code>GetType</code> on itself to get its type. <code>GetType</code> does only need to be implemented once for each class (kind of a static method, really) and is dispatched via the usual virtual function table. Thus only <em>one</em> reference to a <code>Type</code> is required per class, as opposed to per object.</p>

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