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PO"Uncurrying" an instance method in .NET
 

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    <p>Can you create a delegate of an instance method without specifying the instance at creation time? In other words, can you create a "static" delegate that takes as it's first parameter the instance the method should be called on?</p> <p>For example, how can I construct the following delegate using reflection?</p> <pre><code>Func&lt;int, string&gt; = i=&gt;i.ToString(); </code></pre> <p>I'm aware of the fact that I can use methodInfo.Invoke, but this is slower, and does not check for type-correctness until it is called.</p> <p>When you have the <code>MethodInfo</code> of a particular <em>static</em> method, it is possible to construct a delegate using <code>Delegate.CreateDelegate(delegateType, methodInfo)</code>, and all parameters of the static method remain free.</p> <p>As Jon Skeet pointed out, you can simply apply the same to make an open delegate of an instance method if the method is non-virtual on a reference type. Deciding which method to call on a virtual method is tricky, so that's no so trivial, and value-types look like they don't work at all.</p> <p>For value types, <code>CreateDelegate</code> exhibits really weird behavior:</p> <pre><code>var func37 = (Func&lt;CultureInfo,string&gt;)(37.ToString); var toStringMethod = typeof(int).GetMethod("ToString", BindingFlags.Instance | BindingFlags.Public, null, new Type[] {typeof(CultureInfo) }, null); var func42 = (Func&lt;CultureInfo,string&gt;)Delegate.CreateDelegate(typeof(Func&lt;CultureInfo,string&gt;), 42, toStringMethod,true); Console.WriteLine( object.ReferenceEquals(func37.Method,func42.Method)); //true Console.WriteLine(func37.Target);//37 Console.WriteLine(func42.Target);//42 Console.WriteLine(func37(CultureInfo.InvariantCulture));//37 Console.WriteLine(func42(CultureInfo.InvariantCulture));//-201040128... WTF? </code></pre> <p>Calling <code>CreateDelegate</code> with <code>null</code> as the target object throws a binding exception if the instance method belonged to a value type (this works for reference types).</p> <p><em>Some follow-up years later:</em> The incorrectly-bound target that caused <code>func42(CultureInfo.InvariantCulture);</code> to return <code>"-201040128"</code> instead of <code>"42"</code> in my example was memory corruption that could have allowed remote code execution (<a href="http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=cve-2010-1898" rel="nofollow noreferrer">cve-2010-1898</a>); this was fixed in 2010 in the <a href="https://docs.microsoft.com/en-us/security-updates/securitybulletins/2010/ms10-060" rel="nofollow noreferrer">ms10-060</a> security update. Current frameworks correctly print 42! That doesn't make answering this question any easier, but explains the particularly weird behavior in the example.</p>
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