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POIs it possible to cache a value evaluated in a lambda expression?
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  1. POIs it possible to cache a value evaluated in a lambda expression?
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    copied!<p>In the ContainsIngredients method in the following code, is it possible to cache the <em>p.Ingredients</em> value instead of explicitly referencing it several times? This is a fairly trivial example that I just cooked up for illustrative purposes, but the code I'm working on references values deep inside <em>p</em> eg. <em>p.InnerObject.ExpensiveMethod().Value</em></p> <p>edit: I'm using the PredicateBuilder from <a href="http://www.albahari.com/nutshell/predicatebuilder.html" rel="nofollow noreferrer">http://www.albahari.com/nutshell/predicatebuilder.html</a></p> <pre><code>public class IngredientBag { private readonly Dictionary&lt;string, string&gt; _ingredients = new Dictionary&lt;string, string&gt;(); public void Add(string type, string name) { _ingredients.Add(type, name); } public string Get(string type) { return _ingredients[type]; } public bool Contains(string type) { return _ingredients.ContainsKey(type); } } public class Potion { public IngredientBag Ingredients { get; private set;} public string Name {get; private set;} public Potion(string name) : this(name, null) { } public Potion(string name, IngredientBag ingredients) { Name = name; Ingredients = ingredients; } public static Expression&lt;Func&lt;Potion, bool&gt;&gt; ContainsIngredients(string ingredientType, params string[] ingredients) { var predicate = PredicateBuilder.False&lt;Potion&gt;(); // Here, I'm accessing p.Ingredients several times in one // expression. Is there any way to cache this value and // reference the cached value in the expression? foreach (var ingredient in ingredients) { var temp = ingredient; predicate = predicate.Or ( p =&gt; p.Ingredients != null &amp;&amp; p.Ingredients.Contains(ingredientType) &amp;&amp; p.Ingredients.Get(ingredientType).Contains(temp)); } return predicate; } } [STAThread] static void Main() { var potions = new List&lt;Potion&gt; { new Potion("Invisibility", new IngredientBag()), new Potion("Bonus"), new Potion("Speed", new IngredientBag()), new Potion("Strength", new IngredientBag()), new Potion("Dummy Potion") }; potions[0].Ingredients.Add("solid", "Eye of Newt"); potions[0].Ingredients.Add("liquid", "Gall of Peacock"); potions[0].Ingredients.Add("gas", "Breath of Spider"); potions[2].Ingredients.Add("solid", "Hair of Toad"); potions[2].Ingredients.Add("gas", "Peacock's anguish"); potions[3].Ingredients.Add("liquid", "Peacock Sweat"); potions[3].Ingredients.Add("gas", "Newt's aura"); var predicate = Potion.ContainsIngredients("solid", "Newt", "Toad") .Or(Potion.ContainsIngredients("gas", "Spider", "Scorpion")); foreach (var result in from p in potions where(predicate).Compile()(p) select p) { Console.WriteLine(result.Name); } } </code></pre>
 

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