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copied!<p>In .NET, there is no property or method named Value in Object.</p> <p>The way VB.NET handles <code>Object.Value</code> is apparently specific to that language. In C#, for instance, the following code will not even compile:</p> <pre><code> Object o=new Object(); Console.WriteLine(o.Value); </code></pre> <p>with this error:</p> <p>"'object' does not contain a definition for 'Value' and no extension method 'Value' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?)"</p> <p>Note that this has nothing to do with late binding.</p> <p>In VB.NET, on the other hand, the following code <em>will</em> compile without <code>Option Strict</code>:</p> <pre><code> Dim o As New Object() Console.WriteLine(o.Value) </code></pre> <p>but will output a warning: "Late bound resolution; runtime errors could occur."</p> <p>That code will indeed fail at runtime:</p> <p>"Public member 'Value' on type 'Object' not found."</p> <p>VB.NET allowed the code above to compile because it adds extra method calls to the method, as can be seen when we decompile the program:</p> <pre><code>object o = RuntimeHelpers.GetObjectValue(new object()); Console.Write(RuntimeHelpers.GetObjectValue(NewLateBinding.LateGet(o, null, "Value", new object[0], null, null, null))); Console.Write(RuntimeHelpers.GetObjectValue(NewLateBinding.LateGet(o, null, "Value", new object[0], null, null, null))); </code></pre> <p>Note that LateGet supports the late binding feature of VB.NET. It checks whether the given object really does have a <code>Value</code> property. If it does, it gets the Value property and returns that value for Console.Write to output. <code>Object</code> itself doesn't have <code>Value</code>, but other objects do, such as <code>System.Collections.Generic.KeyValuePair<T></code>.</p> <p>The <a href="http://msdn.microsoft.com/en-us/library/microsoft.visualbasic.compilerservices.newlatebinding.lateget.aspx" rel="nofollow">LateGet method</a> of the <a href="http://msdn.microsoft.com/en-us/library/microsoft.visualbasic.compilerservices.newlatebinding.aspx" rel="nofollow">NewLateBinding class</a> "[e]xecutes a late-bound property get or field access call". We can dissect the arguments of LateGet like so:</p> <pre><code>o, // Instance of the object with the property null, // Type (not used) "Value", // Name of the property new object[0], // No arguments null, // No argument names null, // No type arguments ('Value' is not generic) null // N/A; used only on methods with ByRef parameters </code></pre> <p>The <a href="http://msdn.microsoft.com/en-us/library/system.runtime.compilerservices.runtimehelpers.getobjectvalue.aspx" rel="nofollow">RuntimeHelpers.GetObjectValue method</a> boxes the given object, and is thus less relevant here.</p> <p>In C#, late binding can be achieved using code like the following:</p> <pre><code>var o=new System.Collections.Generic.KeyValuePair<int,int>(0,1); Console.WriteLine("{0}",o.GetType().GetProperty("Value").GetValue(o,new object[]{})); </code></pre> <p>I use <code>KeyValuePair</code> here because it contains a <code>Value</code> property. If it were just an <code>Object</code> the code will compile, but will fail at runtime with a NullReferenceException because <code>Value</code> doesn't exist in <code>Object</code>. The code gets the object's type, gets the PropertyInfo associated with the property "Value", and gets the value from the object and the PropertyInfo. <code>LateGet</code> most likely uses a very similar technique.</p>

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