extension-methods

问题 Focus on the strong and generic parts. Let's say I have this extension function: fun <E> Collection<E>.myContains(item: E) : Boolean { // quite pointless, I know, but a simple example return item in this } the intention is to write a function that only accepts types of the collection elements ( E ), but this is not validated by the compiler?! val isItInside: Boolean = listOf(1, 2).myContains("1") happily compiles. My guess is that E is inferred to be Any . How can I enforce this restriction

问题 Does Python have extension methods like C#? Is it possible to call a method like: MyRandomMethod() on existing types like int ? myInt.MyRandomMethod() 回答1: You can add whatever methods you like on class objects defined in Python code (AKA monkey patching): >>> class A(object): >>> pass >>> def stuff(self): >>> print self >>> A.test = stuff >>> A().test() This does not work on builtin types, because their __dict__ is not writable (it's a dictproxy ). So no, there is no "real" extension method

问题 I cannot call an HttpConfiguration extension method: using System.Configuration; using System.Web.Http; ... var config = new HttpConfiguration(); config.MapHttpAttributeRoutes(); // <-- error Error: 'System.Web.Http.HttpConfiguration' does not contain a definition for 'MapHttpAttributeRoutes' and no extension method 'MapHttpAttributeRoutes' accepting a first argument of type 'System.Web.Http.HttpConfiguration' could be found (are you missing a using directive or an assembly reference?) I

问题 I have a slice function which I got here. I was wondering how I can modify it so that if the to string is not found, but it found from it will return the end index of the entire string ( .count-1 ). Right now it's obviously crashing if I call .slice and there is no to string found. extension String { func slice(from: String, to: String) -> String? { return (range(of: from)?.upperBound).flatMap { substringFrom in (range(of: to, range: substringFrom..<endIndex)?.lowerBound).map { substringTo in

问题 This question already has answers here : When do you use extension methods, ext. methods vs. inheritance? (6 answers) Closed 8 days ago . Studying extension methods using the book as an example of expanding the functional structure of an Int32 ( int keyword) in C# (we cannot inherit structures and change the source code in the case of Int32 ), I realized that extension methods are needed for three things: If inheritance is not possible, as in the case with sealed classes; In case of the

问题 I'm accustomed to extension methods being presented by intellisense, after the 'this' type is keyed-in. But when I try this with HtmlHelper, the extension methods don't show - even though the 'using' statement is present. Why is this? To clarify, I'm doing this test from within a regular .cs file, rather than a .cshtml file. No good reason, I'm simply playing with the MVC namespace and language to "see how it ticks." I still don't know why the intellisense doesn't pick up all 4000 extensions

问题 I'm accustomed to extension methods being presented by intellisense, after the 'this' type is keyed-in. But when I try this with HtmlHelper, the extension methods don't show - even though the 'using' statement is present. Why is this? To clarify, I'm doing this test from within a regular .cs file, rather than a .cshtml file. No good reason, I'm simply playing with the MVC namespace and language to "see how it ticks." I still don't know why the intellisense doesn't pick up all 4000 extensions

问题 I've been trying and trying to make my generic extension methods work, but they just refuse to and I can't figure out why . This thread didn't help me, although it should. Of course I've looked up how to, everywhere I see they say it's simple and it should be in this syntax: (On some places I read that I need to add "where T: [type]" after the parameter decleration, but my VS2010 just says that's a syntax error.) using System.Collections.Generic; using System.ComponentModel; public static

问题 I have a base abstract class to implement template method pattern. public abstract class OptionalParameter { //Template Method Pattern public string GenerateQueryString() { return this.GenerateQueryStringWithParameters(); } } And I have an extension method for all OptionalParameter type. public static class OptionalParameterExtensions { public static string GenerateQueryStringWithParameters(this OptionalParameter optionalParameters) { } } I inherited a class from OptionalParameter named

问题 I have a base abstract class to implement template method pattern. public abstract class OptionalParameter { //Template Method Pattern public string GenerateQueryString() { return this.GenerateQueryStringWithParameters(); } } And I have an extension method for all OptionalParameter type. public static class OptionalParameterExtensions { public static string GenerateQueryStringWithParameters(this OptionalParameter optionalParameters) { } } I inherited a class from OptionalParameter named