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1533364
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2009-10-07T18:29:41.223
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2013-10-12T14:46:01.483
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2013-10-12T14:46:01.483
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<p>You can use expression tree as a code builder with a higher abstraction level then assembly emit and faster then CodeCompiler. Here is some proof of the concept that i used to convince our team to use them as a replacement for CodeCompiler.</p> <pre><code>[TestClass] public class WhenINeedToAccessPropertiesByNameHavingATypeReference { public class SomeCategoryData { public DateTime CreatedDate { get; set; } } [TestMethod] public void ICanDoThatWithAnExpressionAndItPerformsWell() { // INIT var someCategoryData = Enumerable.Range(1970, 100).Select(year => new SomeCategoryData { CreatedDate = new DateTime(year, 1, 1) }).Cast<object>(); var t = typeof(SomeCategoryData); // or it can be: t = someCategoryData.First().GetType(); var compiled = Stopwatch.StartNew(); // ACT var filter = AccessPropertyByNameInCompiledMannerSomehow(t, "CreatedDate"); // ASSERT Trace.WriteLine(string.Format("compiled in: {0}", compiled.Elapsed)); Assert.IsTrue(compiled.ElapsedMilliseconds < 3, "compiles fast enough"); var executed = Stopwatch.StartNew(); // ACT List<object> result = null; for (var i = 0; i < 10000; i++) { result = someCategoryData.Where(d => filter(d, new DateTime(2000, 1, 1), new DateTime(2009, 1, 1))) .ToList(); } executed.Stop(); Trace.WriteLine(string.Format("executed in: {0}", executed.Elapsed)); // ASSERT Assert.AreEqual(10, result.Count, "insure compiled code actually works"); Assert.IsTrue(executed.ElapsedMilliseconds < 300, "runs fast enough"); } private static Func<object, DateTime, DateTime, bool> AccessPropertyByNameInCompiledMannerSomehow(Type t, string fieldToFilterBy) { var objectParameter = Expression.Parameter(typeof(object), "p"); var instance = Expression.Convert(objectParameter, t); var lower = Expression.Parameter(typeof(DateTime), "l"); var upper = Expression.Parameter(typeof(DateTime), "u"); var composite = Expression.Lambda<Func<object, DateTime, DateTime, bool>>( Expression.And( Expression.LessThanOrEqual( lower, Expression.PropertyOrField(instance, fieldToFilterBy) ), Expression.GreaterThanOrEqual( upper, Expression.PropertyOrField(instance, fieldToFilterBy) ) ), objectParameter, lower, upper ); return composite.Compile(); } } </code></pre>
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1. POWhats a good use case for .net 4.0 Expression Trees?
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1. USnawfal
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1. USGeorge Polevoy
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