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POCreate a constructor call using Reflection Emit that passes a Func<> as a parameter
 

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  1. POCreate a constructor call using Reflection Emit that passes a Func<> as a parameter
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    <p>I'm hoping someone can point me in the right direction with the following problem. </p> <p>I am working on a project where the types are generated using Reflection.Emit, all has been working fine until a requirement arose where I needed to pass a Func&lt;> into a constructor of a new object as below.</p> <pre><code>public class SearchTerm : IEntity { private readonly NavigationProperty&lt;Item&gt; _item; public SearchTerm() { _item = new NavigationProperty&lt;Item&gt;(() =&gt; ItemIds); } public string[] ItemIds { get; set; } } </code></pre> <p>Using Linqpad I can see the IL output is as follows:</p> <pre><code>SearchTerm.&lt;.ctor&gt;b__0: IL_0000: ldarg.0 IL_0001: call UserQuery+SearchTerm.get_ItemIds IL_0006: stloc.0 // CS$1$0000 IL_0007: br.s IL_0009 IL_0009: ldloc.0 // CS$1$0000 IL_000A: ret SearchTerm..ctor: IL_0000: ldnull IL_0001: stloc.0 IL_0002: ldarg.0 IL_0003: call System.Object..ctor IL_0008: nop IL_0009: nop IL_000A: ldarg.0 IL_000B: ldloc.0 IL_000C: brtrue.s IL_001D IL_000E: ldarg.0 IL_000F: ldftn UserQuery+SearchTerm.&lt;.ctor&gt;b__0 IL_0015: newobj System.Func&lt;System.Collections.Generic.IEnumerable&lt;System.String&gt;&gt;..ctor IL_001A: stloc.0 IL_001B: br.s IL_001D IL_001D: ldloc.0 IL_001E: newobj UserQuery&lt;UserQuery+Item&gt;+NavigationProperty`1..ctor IL_0023: stfld UserQuery+SearchTerm._item IL_0028: nop IL_0029: ret </code></pre> <p>The problem I have is that I'm not sure how to define the delegate within IL.</p> <p>I have tried the following</p> <pre><code>var method = typeBuilder.DefineMethod("func", MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig | MethodAttributes.Virtual, typeof(IEnumerable&lt;string&gt;), Type.EmptyTypes); var methodIl = method.GetILGenerator(); methodIl.Emit(OpCodes.Ldarg_0); methodIl.Emit(OpCodes.Call, dictionary["get_ItemIds"]); methodIl.Emit(OpCodes.Ret); </code></pre> <p>Then trying to create the delegate the following throws "Not Supported Exception" with the error "Derived classes must provide an implementation."</p> <pre><code>var funcType = typeof(Func&lt;,&gt;).MakeGenericType(typeBuilder, typeof(IEnumerable&lt;string&gt;)); method.CreateDelegate(funcType); </code></pre> <p>I have also tried using Delegate.CreateDelegate and DynamicMethod which both require the type to have been created before using them.</p> <p>Any suggestion on what I might be doing wrong are greatly appreciated.</p>
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