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POC# construct lambda using Expression.Call doesn't like certain types as params?
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  1. POC# construct lambda using Expression.Call doesn't like certain types as params?
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    copied!<p>For various reasons I'm constructing a C# lambda dynamically using the expression tree facilities. e.g. I can make a Func&lt;string,bool&gt; at runtime as shown in the following snippet. </p> <pre><code> public static bool myMethod( object obj ) { … } // Construct a Func&lt;string,bool&gt; var myMethod = GetType().GetMethod("myMethod"); var lambdaParams = new ParameterExpression[] {Expression.Parameter(typeof (string))}; var callMyMethod = Expression.Call(myMethod, lambdaParams); var lambda = Expression.Lambda(typeof(Func&lt;string,bool&gt;), callMyMethod, lambdaParams); var del = (Func&lt;string,bool&gt;)lambda.Compile(); del("foo"); // works </code></pre> <p>However if I use the same code to try to make a Func&lt;int,bool&gt; or a Func&lt;DateTime,bool&gt; it blows up where indicated with the following strange exception:</p> <pre><code> // Construct a Func&lt;DateTime,bool&gt; or perhaps a struct type fails... why? var myMethod = GetType().GetMethod("myMethod"); var lambdaParams = new ParameterExpression[] {Expression.Parameter(typeof (DateTime))}; var callMyMethod = Expression.Call(myMethod, lambdaParams); // Blows up here… System.ArgumentException: Expression of type 'System.DateTime' cannot be used for parameter of type 'System.Object' of method 'Boolean myMethod(System.Object)' </code></pre> <p>So, string works and List&lt;string&gt; works but int32 does not work nor does DateTime. What is going on? I don't know how the deep internals of C# work but I am guessing it's due to int really being handled as a primitive and maybe DateTime (being a struct) as well...</p> <p>Any help with this would be greatly appreciated.</p> <p>thanks, Pat</p>
 

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