extension-methods | 易学教程

C#: Best practice for validating “this” argument in extension methods

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问题 Let's say I have an extension method public static T TakeRandom<T>(this IEnumerable<T> e) { ... To validate the argument e, should I: A) if (e == null) throw new NullReferenceException() B) if (e == null) throw new ArgumentNullException("e") C) Not check e What's the consensus? My first thought is to always validate arguments, so thrown an ArgumentNullException. Then again, since TakeRandom() becomes a method of e, perhaps it should be a NullReferenceException. But if it's a

What is difference between extension method and static method?

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问题 What is the difference between an extension method and a static method ? I have two classes like this : public static class AClass { public static int AMethod(string ....) { } } and public static class BClass { public static int BMethod(this string ....) { } } I can use these like AClass.AMethod('...'); or '...'.BMethod(); Which is proposed ? 回答1: An extension method is still a static method. You can use it exactly as you'd use a normal static method. The only difference is that an extension

How does VB.NET compiler choose which extension overload to run?

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问题 Got an interesting oddity - thought someone might be able to help. This came out of some fun with nullable types from this question: How to check if an object is nullable? Option Strict On Module Test ' Call this overload 1 <Extension()> Function IsNullable(obj As ValueType) As Boolean Return False End Function ' Call this overload 2 <Extension()> Function IsNullable(Of T As {Structure})(obj As Nullable(Of T)) As Boolean Return True End Function Sub Test() ' a is an integer! Dim a As Integer

IQueryable (non generic) : missing Count and Skip ? it works with IQueryable<T>

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问题 i have an extension method which a person was really helpful to give me... it does an orderby on IQueryable ... but i wanted one to do a normal IQueryable (non generic) Here is the code, The count and Skip and i think Take are missing . public static IQueryable GetPage(this IQueryable query, int page, int pageSize, out int count) { int skip = (int)((page - 1) * pageSize); count = query.Count(); //COUNT DOESN'T EXIST return query.Skip(skip).Take((int)pageSize); // NEITHER SKIP } Here is the

Disadvantages of extension methods?

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Extension method is a really helpful feature that you can add a lot of functions you want in any class. But I am wondering if there is any disadvantage that might bring troubles to me. Any comments or suggestions? The way that extension methods are imported (i.e. a whole namespace at a time) isn't granular. You can't import one extension from a namespace without getting all the rest. It's not immediately obvious from the source code where the method is defined. This is also an advantage - it means you can make your code look consistent with the rest of the methods on the type, even if you can

How to Mock (with Moq) Unity methods

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问题 Extension methods are not good for testing (that's described here: Mocking Extension Methods with Moq, http://www.clariusconsulting.net/blogs/kzu/archive/2009/12/22/Howtomockextensionmethods.aspx). But probably there are some solutions for mocking of Unity methods? In my case I have the following function: public class MyManager { public MyManager(IUnityContainer container) : base(container) { } public IResult DoJob(IData data) { IMyLog log = MyContainer.Resolve<IMyLog>(); ... use log.Id ...

Is it possible define an extension operator method?

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问题 is it possible to define an extension method that at the same time is an operator? I want for a fixed class add the possibility to use a known operator that actually can't be applied. For this particular case i want to do this: somestring++; //i really know that this string contains a numeric value And i don't want to spread types conversions for all the code. I know that i could create wrapper class over an string and define that operator but i want to know if this kind of thing is possible

Which mechanism is a better way to extend Dictionary to deal with missing keys and why?

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问题 There is a minor annoyance I find myself with a lot - I have a Dictionary<TKey, TValue> that contains values that may or may not be there. So normal behaviour would be to use the indexer, like this: object result = myDictionary["key"]; However, if "key" is not in the dictionary this throws a KeyNotFoundException , so you do this instead: object val; if (!myDictionary.TryGetValue("key", out val)) { val = ifNotFound; } Which is fine, except that I can have a load of these in a row - TryGetValue

Generic Map/Reduce List Extensions in C#

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I am writing a few extensions to mimic the map and reduce functions in Lisp. public delegate R ReduceFunction<T,R>(T t, R previous); public delegate void TransformFunction<T>(T t, params object[] args); public static R Reduce<T,R>(this List<T> list, ReduceFunction<T,R> r, R initial) { var aggregate = initial; foreach(var t in list) aggregate = r(t,aggregate); return aggregate; } public static void Transform<T>(this List<T> list, TransformFunction<T> f, params object [] args) { foreach(var t in list) f(t,args); } The transform function will cut down on cruft like: foreach(var t in list) if

What is the easiest way to get the property value from a passed lambda expression in an extension method for HtmlHelper?

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I am writing a dirty little extension method for HtmlHelper so that I can say something like HtmlHelper.WysiwygFor(lambda) and display the CKEditor. I have this working currently but it seems a bit more cumbersome than I would prefer. I am hoping that there is a more straight forward way of doing this. Here is what I have so far. public static MvcHtmlString WysiwygFor<TModel, TProperty>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TProperty>> expression) { return MvcHtmlString.Create(string.Concat("<textarea class=\"ckeditor\" cols=\"80\" id=\"", expression.MemberName(), "\" name=\