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POUniquely identifying anonymous method with parameters of Func body
 

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  1. POUniquely identifying anonymous method with parameters of Func body
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    <p>I'm trying to write some magic code for handling caching that may or may not be possible. Basically, the idea is to have a CacheManager class with a static method which accepts an Func to execute as a parameter. In the static method's body, it would be able to execute that Func and cache the results using a cache key that uniquely identifies the internals of that Func passed (an anonymous method with 0 or more parameters). Subsequent calls to that static method with the same arguments provided would result in the same cache key and return the cached results.</p> <p>I need a way of uniquely identifying the anonymous function that is passed in.</p> <p><em><strong>Edit:</strong> Expression provided the answer once I adjusted the anonymous function syntax.</em> </p> <p>I'm worried about the performance impact of having to compile the expression at run-time. Given this is an attempt to support caching for performance it'd be silly for the compile to take any significant amount of time. Any thoughts? </p> <p><strong>Basic repository for testing:</strong></p> <pre><code>public class Product { public int ID { get; set; } public string Name { get; set; } } public class ProductRepository { private List&lt;Product&gt; products { get; set; } public ProductRepository() { products = new List&lt;Product&gt;() { new Product() { ID = 1, Name = "Blue Lightsaber" }, new Product() { ID = 2, Name = "Green Lightsaber" }, new Product() { ID = 3, Name = "Red Lightsaber" } }; } public Product GetByID(int productID) { return products.SingleOrDefault(p =&gt; p.ID == productID); } } </code></pre> <p><strong>CacheManager:</strong></p> <pre><code>public class CacheManager { public static TResult Get&lt;TResult&gt;(Expression&lt;Func&lt;TResult&gt;&gt; factory) { if (factory == null) throw new ArgumentNullException("factory"); var methodCallExpression = factory.Body as MethodCallExpression; if (methodCallExpression == null) throw new ArgumentException("factory must contain a single MethodCallExpression."); string cacheKey = "|Repository:" + methodCallExpression.Method.DeclaringType.FullName + "|Method:" + methodCallExpression.Method.Name + "|Args"; foreach (var arg in methodCallExpression.Arguments) { cacheKey += ":" + (arg is ConstantExpression ? ((ConstantExpression)arg).Value : Expression.Lambda(arg).Compile().DynamicInvoke()); } if (HttpContext.Current.Cache[cacheKey] == null) { HttpContext.Current.Cache[cacheKey] = factory.Compile().Invoke(); } return (TResult)HttpContext.Current.Cache[cacheKey]; } } </code></pre> <p><strong>Usage:</strong></p> <pre><code>ProductRepository productRepository = new ProductRepository(); int productID = 1; Product product; // From repo product = CacheManager.Get&lt;Product&gt;(() =&gt; productRepository.GetByID(1)); // From cache product = CacheManager.Get&lt;Product&gt;(() =&gt; productRepository.GetByID(productID)); </code></pre>
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    1. USbenmccallum
    1. USbenmccallum
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      1. USDaniel Hilgarth
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    1. COIs the body of the action restricted in any way? Or could it be basically any arbitrary code?
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      1. USDaniel Hilgarth
    2. COThat was going to be my next problem... is it even possible to enforce anything there?? I could probably put a restriction on the TInstance type. It would be nice to enforce that the Action body was a single assignment statement to my `out` argument to reduce the chance of something volatile being passed as the Action (assuming that is the syntax required if a final solution is achieved).
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      1. USbenmccallum
    3. COYou can't enforce it at compile time, you can only enforce it at runtime with the help of expressions. One thought: Why the strange syntax with assigning to the variable and having the same one as an out parameter? Why not simply use a `Func<TRepository, TResult>` and change `GetValue` to this signature: `TResult GetValue<TRepository, TResult>(TRepository repository, Func<TRepository, TResult> valueFactory)`? This would actually work, your current code wouldn't.
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      1. USDaniel Hilgarth
 

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