Code Syntax Style: Implicit/Explicit Typing ('var' Keyword)

Enforcing preferences of using 'var' keyword

JetBrains Rider checks all local variables for compliance with your preferences and if they do not comply, JetBrains Rider highlights such declarations and suggests the corresponding quick-fix or fix in scope.

By default, JetBrains Rider's preferences say that 'var' keyword is preferred:

If you change your preference, JetBrains Rider will help you to use explicit types:

Another option to enforce preferences of 'var' keyword usage in a bulk mode is code cleanup. You can either run code cleanup with the default profile Default: Full Cleanup or run the cleanup with a custom profile solely targeted at your specific task as described below.

To apply preferences of using 'var' keyword with custom Code Cleanup profile

1. Press Ctrl+Alt+S, or alternatively choose File | Settings on Windows and Linux or JetBrains Rider | Preferences on macOS.
2. Go to the Code Cleanup settings page: Editor | Code Cleanup.
3. Create a new profile as described in the To create a new custom cleanup profile section. In the Selected profile settings section for the new profile, tick the Enforce 'var' keyword usage settings check box. Optionally, you can enable other code cleanup tasks in this profile.
4. Click Save to apply the modifications and let JetBrains Rider choose where to save them, or save the modifications to a specific settings layer using the Save To drop-down list. For more information, see layer-based settings.
5. Select the scope where you want to enforce your preferences:
   • Set the caret anywhere in the file to enforce your preferences to the file.
   • Select one or more items in the Solution Explorer to enforce your preferences in the files under these nodes and their child items.
6. Choose Code | Code Cleanup in the main menu.
7. In the Code Cleanup dialog that opens, select the newly created profile.
8. Click OK. JetBrains Rider will enforce your preferences in the selected scope.

Configuring preferences of using 'var' keyword

Your 'var' keyword usage preferences are saved using the mechanism of layer-based settings. Among other things, this mechanism allows you to maintain different preferences for different solutions as well as to keep these preferences under a VCS and automatically share them with your team members.

To configure preferences of using 'var' keyword

1. Go to the Editor | Code Style | C# page of JetBrains Rider settings (Ctrl+Alt+S), and then select the Code Style tab.
2. Modify settings in the 'var' usage in declarations category according to your coding practices/standards. You can set different preferences of using 'var' or explicit type for different types:
   • For built-in types — applies to C# built-in types.
   • For simple types — applies to types without generic parameters.
   • Elsewhere — applies to generic types and deconstruction declarations.
   For each of these preferences you can opt for using 'var', explicit type, or 'var' when evident, which means that 'var' should be only used for variables initialized as creation of objects, arrays, and literals or explicit casts.
3. By default, JetBrains Rider will suggest joined notation for multiple var's in deconstruction declarations, e.g. var (x, y) = GetTuple();. You can select Prefer separate declarations for deconstructed variables to opt for separate notation, e.g. (var x, var y) = GetTuple();.
4. You can also select Use 'var' keyword for discards to always use var with discards where appropriate thus making sure that there are no conflicts with variables in the scope that may be named _.
5. The selectors in the right column allow you to set severity levels of code inspections detecting code that differs from your preferences.
6. Click Save to apply the modifications and let JetBrains Rider choose where to save them, or save the modifications to a specific settings layer using the Save To drop-down list. For more information, see layer-based settings.