{"id":1059,"date":"2023-03-18T19:08:06","date_gmt":"2023-03-18T12:08:06","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=1059"},"modified":"2023-03-18T20:18:17","modified_gmt":"2023-03-18T13:18:17","slug":"csharp-extension-methods","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-tutorial\/csharp-extension-methods\/","title":{"rendered":"C# Extension Methods"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you&#8217;ll learn about C# extension methods and how to use them to extend any type with additional methods. <\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Introduction to C# extension methods<\/h2>\n\n\n\n<p>To add a method to a <a href=\"https:\/\/csharptutorial.net\/csharp-tutorial\/csharp-class\/\">class<\/a>, we often subclass the existing class and add the method to the derived class. <\/p>\n\n\n\n<p>C# introduced a new feature called extension methods that allows you to add new methods to an existing type (or class) without the need of using <a href=\"https:\/\/csharptutorial.net\/csharp-tutorial\/csharp-inheritance\/\">inheritance<\/a>.<\/p>\n\n\n\n<p>An extension method is a <a href=\"https:\/\/csharptutorial.net\/csharp-tutorial\/csharp-static-method\/\">static method<\/a> but it is called as if it was an instance method on the extended type.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Creating C# extension methods<\/h2>\n\n\n\n<p>To create an extension method, you define a <a href=\"https:\/\/csharptutorial.net\/csharp-tutorial\/csharp-static-classes\/\">static class<\/a> that contains the extension method. For example, the following creates an extension method on the <code>string<\/code> type:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">using System.Globalization;\n\n<span class=\"hljs-keyword\">static<\/span> <span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">StringExtensions<\/span>\n<\/span>{\n    public <span class=\"hljs-keyword\">static<\/span> string ToTitleCase(<span class=\"hljs-keyword\">this<\/span> string value)\n    {\n        <span class=\"hljs-keyword\">return<\/span> CultureInfo.CurrentCulture.TextInfo.ToTitleCase(value);\n    }\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>How it works.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>First, define the static class called <code>StringExtensions<\/code>.<\/li>\n\n\n\n<li>Second, define the extension method <code>ToTitleCase()<\/code> as a static method of the <code>StringExtensions<\/code> class. The extension method uses <code><a href=\"https:\/\/csharptutorial.net\/csharp-tutorial\/csharp-this\/\">this<\/a><\/code> keyword before the first parameter. In this example, the <code>ToTitleCase()<\/code> method uses the current culture&#8217;s text info to convert a string to a title case.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Using C# extension methods<\/h2>\n\n\n\n<p>The following program demonstrates how to call the <code>ToTitleCase()<\/code> extension method on a string:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">using System.Globalization;\n\n<span class=\"hljs-keyword\">static<\/span> <span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">StringExtensions<\/span>\n<\/span>{\n    public <span class=\"hljs-keyword\">static<\/span> string ToTitleCase(<span class=\"hljs-keyword\">this<\/span> string value)\n    {\n        <span class=\"hljs-keyword\">return<\/span> CultureInfo.CurrentCulture.TextInfo.ToTitleCase(value);\n    }\n}\n\n<span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Program<\/span>\n<\/span>{\n    public <span class=\"hljs-keyword\">static<\/span> <span class=\"hljs-keyword\">void<\/span> Main(string&#91;] args)\n    {\n        <span class=\"hljs-keyword\">var<\/span> message = <span class=\"hljs-string\">\"C# extension methods are cool\"<\/span>;\n        <span class=\"hljs-keyword\">var<\/span> result = message.ToTitleCase();\n\n        Console.WriteLine(result);\n    }\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php\">C<span class=\"hljs-comment\"># Extension Methods Are Cool<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\">A more practical example of the C# extension method<\/h2>\n\n\n\n<p>The following example demonstrates how to use extension methods to extend the int type by adding two methods <code>IsEven()<\/code> and <code>IsOdd()<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php\"><span class=\"hljs-keyword\">static<\/span> <span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">IntExtensions<\/span>\n<\/span>{\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">static<\/span> bool IsEven(this int value)\n    {\n        <span class=\"hljs-keyword\">return<\/span> value % <span class=\"hljs-number\">2<\/span> == <span class=\"hljs-number\">0<\/span>;\n    }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">static<\/span> bool IsOdd(this int value)\n    {\n        <span class=\"hljs-keyword\">return<\/span> !IsEven(value);\n    }\n}\n\n<span class=\"hljs-class\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Program<\/span>\n<\/span>{\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">static<\/span> void Main(string&#91;] args)\n    {\n        int&#91;] numbers = { <span class=\"hljs-number\">3<\/span>, <span class=\"hljs-number\">5<\/span>, <span class=\"hljs-number\">6<\/span>, <span class=\"hljs-number\">2<\/span>, <span class=\"hljs-number\">7<\/span>, <span class=\"hljs-number\">8<\/span> };\n\n        <span class=\"hljs-keyword\">foreach<\/span> (<span class=\"hljs-keyword\">var<\/span> number in numbers)\n        {\n            <span class=\"hljs-keyword\">if<\/span> (number.IsEven())\n            {\n                Console.WriteLine(number);\n            }\n        }\n\n    }\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs\">6\n2\n8<\/code><\/span><\/pre>\n\n\n<p>In this example, the <code>IsEven()<\/code> method returns <code>true<\/code> if the number is even and <code>false<\/code> otherwise. The <code>IsOdd()<\/code> method is the reverse of the <code>IsEven()<\/code> method.<\/p>\n\n\n\n<p>In the <code>Main()<\/code> method of the <code>Program<\/code> class, we define a list of integers, iterate over its elements using a <a href=\"https:\/\/csharptutorial.net\/csharp-tutorial\/csharp-foreach\/\">foreach<\/a>, and write the even number to the console.  We use the <code>IsEven()<\/code> extension method to check if a number is even or not.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Advantages of C# extension methods<\/h2>\n\n\n\n<p>Extension methods have the following advantages:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Allow you to add functionality to the types that you don&#8217;t control such as .NET classes without the need of subclassing them.<\/li>\n\n\n\n<li>Make your code cleaner and more readable by keeping related methods in one place.<\/li>\n\n\n\n<li>Better discoverability: When working with an object, you can find all its extension methods via IntelliSense.<\/li>\n<\/ul>\n\n\n\n<p>The following picture shows the available extension methods (<code>IsEven<\/code> &amp; <code>IsOdd<\/code>) of the integer type that we defined in the previous example:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"519\" height=\"168\" src=\"https:\/\/csharptutorial.net\/wp-content\/uploads\/2023\/03\/csharp-extension-methods.png\" alt=\"\" class=\"wp-image-1068\" srcset=\"https:\/\/www.csharptutorial.net\/wp-content\/uploads\/2023\/03\/csharp-extension-methods.png 519w, https:\/\/www.csharptutorial.net\/wp-content\/uploads\/2023\/03\/csharp-extension-methods-300x97.png 300w\" sizes=\"auto, (max-width: 519px) 100vw, 519px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>C# extension methods allow you to extend an existing type without using inheritance.<\/li>\n<\/ul>\n<div class=\"helpful-block-content\" data-title=\"\">\n\t<header>\n\t\t<div class=\"wth-question\">Was this tutorial helpful ?<\/div>\n\t\t<div class=\"wth-thumbs\">\n\t\t\t<button\n\t\t\t\tdata-post=\"1059\"\n\t\t\t\tdata-post-url=\"https:\/\/www.csharptutorial.net\/csharp-tutorial\/csharp-extension-methods\/\"\n\t\t\t\tdata-post-title=\"C# Extension 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tutorial, you&#8217;ll learn about C# extension methods and how to use them to extend any type with additional methods. 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