{"id":170,"date":"2009-02-23T12:00:18","date_gmt":"2009-02-23T10:00:18","guid":{"rendered":"http:\/\/mariusbancila.ro\/blog\/?p=170"},"modified":"2009-02-25T08:29:55","modified_gmt":"2009-02-25T06:29:55","slug":"optional-and-named-parameters-in-c-40","status":"publish","type":"post","link":"https:\/\/mariusbancila.ro\/blog\/2009\/02\/23\/optional-and-named-parameters-in-c-40\/","title":{"rendered":"Optional and Named Parameters in C# 4.0"},"content":{"rendered":"

So far, C#, unlike C++, did not support optional arguments<\/i>. For instance, suppose you need a function to print log a message, that can add a new line or not after writing the message. Most of the times you want a new line, so you don’t want to specify that for most of the calls. Until now, the only possibility was using overloaded functions, with different parameters.<\/p>\n

\r\nclass Logger\r\n{\r\n   public void LogMessage(string error, bool addNewLine)\r\n   {\r\n      Console.Write(error);\r\n      if (addNewLine) Console.WriteLine();\r\n   }\r\n\r\n   public void LogMessage(string error)\r\n   {\r\n      LogMessage(error, true);\r\n   }\r\n};\r\n\r\nclass Program\r\n{\r\n   static void Main(string[] args)\r\n   {\r\n      Logger log = new Logger();\r\n      log.LogMessage(\"trying to connect...\", false);\r\n      \/\/ do more stuff here\r\n      log.LogMessage(\"SUCCESS\");\r\n   }\r\n}\r\n<\/pre>\n
\r\ntrying to connect...SUCCESS\r\nPress any key to continue . . .\r\n<\/pre>\n
C# 4.0, that will be released with Visual Studio 2010, and is for now available with the Visual Studio 2010 CTP<\/a>, supports, just like C++, optional arguments. So instead of using overloaded functions, you can specify a default value for a parameter. When doing the call, if you don’t provide a value for the argument, the default one will be used.<\/p>\n
The Logger class below is identical from the functionality point of view with the one above. (The previous Main() function doesn’t have to change.)<\/p>\n
\r\nclass Logger\r\n{\r\n   public void LogMessage(string error, bool addNewLine = true)\r\n   {\r\n      Console.Write(error);\r\n      if (addNewLine) Console.WriteLine();\r\n   }\r\n};\r\n<\/pre>\n
The only restriction is that optional parameters have to appear in the function after all required parameters. In other words, this is not legal:<\/p>\n
\r\nclass foo\r\n{\r\n   public void func(int a, int b = 0, int c)\r\n   {\r\n   }\r\n}\r\n<\/pre>\n
\r\nerror CS1737: Optional parameters must appear after all required parameters\r\n<\/pre>\n
Considering this implementation of foo<\/p>\n
\r\nclass foo\r\n{\r\n   public void func(int a, int b = 0, int c = 1)\r\n   {\r\n   }\r\n}\r\n<\/pre>\n
the following calls can be made:<\/p>\n
\r\nvar f = new foo();\r\nf.func(42, 3, 4);          \/\/ f.func(42, 3, 4)\r\nf.func(42);                \/\/ f.func(42, 0, 1)\r\nf.func(42, 100);           \/\/ f.func(42, 100, 1)\r\n<\/pre>\n
But this is not all. C# 4.0 brings another feature: named parameters<\/i> (and this does not exist in C++). It means that when you make a call, you can specify an argument by its name, not by position. In this case you use the parameter’s name followed by ‘:’ and the value. Here are several examples:<\/p>\n
\r\nvar f = new foo();\r\nf.func(42, c: 4);          \/\/ f.func(42, 0, 4)\r\nf.func(42, c: 4, b: 3);    \/\/ f.func(42, 3, 4)\r\nf.func(c: 3, a: 1, b: 2);  \/\/ f.func(1, 2, 3)\r\n<\/pre>\n
Of course, this can be used regardless the function has optional parameters or not. However, I would not use this feature for anything else than specifying an optional parameter when I would have to first suply values for other several optional parameters. In other words:<\/p>\n
\r\nvar f = new foo();\r\nf.func(42, c: 4);          \/\/ this is good, skip b, provide value for c\r\nf.func(42, c: 4, b: 3);    \/\/ don't like this, rather call f.func(42, 3, 4)\r\nf.func(c: 3, a: 1, b: 2);  \/\/ don't like this, rather call f.func(1, 2, 3)\r\n<\/pre>\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
So far, C#, unlike C++, did not support optional arguments. For instance, suppose you need a function to print log a message, that can add a new line or not after writing the message. Most of the times you want a new line, so you don’t want to specify that for most of the calls. … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[11,20,10],"tags":[451,90,80,79,81,89],"class_list":["post-170","post","type-post","status-publish","format-standard","hentry","category-csharp","category-ctps-betas","category-visual-studio","tag-c","tag-ctp","tag-named","tag-optional","tag-parameters","tag-vs2010"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t