Code Syntax Style: Object Creation ('new()' vs 'new T()')
Last modified: 21 July 2022Starting with C# 9.0, you can create objects with the target-typed new operator without explicit type specification when the type can be inferred, that is List<string> _myList = new(); instead of List<string> _myList = new List<string>();.
Depending on the context, the optional type specification can either clutter your code with redundant information or, on the contrary, improve the readability.
Therefore, ReSharper provides two code style preferences for object creation expressions:
when created type is evident from usage, like in the following cases:
Initializers of fields/constants/properties/events
private Test field = new()Initializers of local variables when explicit type is preferred
Test local = new()Return values of expression-bodied members
public List <Test> M() => new()Values within array initializer
new Test[] { new(), new() }Values within collection initializer
new List <Test> { new(), new() }Default parameter values
void M(TestStruct arg = new()) { }
when created type is not evident (for example, in return statements).
ReSharper helps you enforce style preferences for object creation expressions in the existing code and takes your preferences into account when it produces new code with code completion and code generation features, applies code templates and performs refactorings.
Enforce preferences for object creation expressions
By default, ReSharper highlights type specifications as redundant in evident cases and helps removing them:
On the other hand, in non-evident cases ReSharper suggests explicitly specifying the created type:
If you prefer other styles for the new operator in your code, you can change the corresponding preferences.
Another option to enforce your preferences for object creation expressions in a bulk mode is code cleanup. You can either run code cleanup with one of the built-in profiles Full Cleanup or Reformat & Apply Syntax Style, or create and run a custom profile solely targeted at your specific task as described below.
note
Preferences for object creation expressions are not applied to generated code. By default, ReSharper provides the list of file masks and regions for generated code typically produced by Visual Studio (for example, Windows Form Designer-generated code). If necessary, you can edit the list of generated items on the Code Inspection | Generated Code page of ReSharper options (Alt+R, O).
Apply object creation style with custom Code Cleanup profile
Select ReSharper | Options from the main menu or press Alt+R O.
Go to the cleanup profiles settings page: Code Editing | Code Cleanup | Profiles.
Create a new profile as described in the Create a new custom cleanup profile section. In the Selected profile settings section for the new profile, tick the Apply object creation style ('new()' vs 'new T()') checkbox. Optionally, you can enable other code cleanup tasks in this profile.
Click Save in the Options dialog to apply the modifications and let ReSharper choose where to save them, or save the modifications to a specific settings layer using the Save To list. For more information, see manage and share resharper settings.
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.
Do one of the following:
Press Ctrl+E C or choose ReSharper | Edit | Cleanup Code... from the main menu .
Right-click anywhere in the text editor or right-click the selection and choose Cleanup Code in the context menu.
In the Code Cleanup dialog that opens, select the newly created profile .
Click Run. ReSharper will enforce your preferences in the selected scope.
If you want to enforce style preferences for object creation expressions without opening the Code Cleanup dialog to choose a profile, you can bind the created profile to the silent cleanup and run it by pressing Ctrl+E F. You can also create a custom cleanup profile that would combine arranging object creation expressions with other code style tasks.
To apply preferences for object creation expressions together with all other formatting and syntax style rules to the selected code block, Alt+Enter and choose Reformat and cleanup | Reformat & apply syntax style.
You can enforce style preferences for object creation expressions every time you save changes in a file to make sure that your edits always comply with your code style.
Automatically enforce style preferences for object creation expressions on saving changes
Select ReSharper | Options from the main menu or press Alt+R O.
Go to the cleanup profiles settings page: Code Editing | Code Cleanup | Profiles.
Select your custom Code Cleanup profile and click Set as default (the default profile is also used for silent cleanup).
Go to the Code Editing | Code Cleanup | General options page and select Automatically run cleanup when saving a file.
Optionally, you can restrict automatic cleanup to specific files by a file mask. You can also select Only changed parts of file to make sure that cleanup is applied to the code affected by your changes, and the rest of the code in the file is not modified.
Click Save in the dialog to apply the modifications and let ReSharper choose where to save them, or save the modifications to a specific settings layer using the Save To list. For more information, see manage and share resharper settings.
The next time you finish editing and save the file (Ctrl+S) or all files (Ctrl+Shift+S), ReSharper will clean up the affected files using the selected profile. If the default cleanup profile is not selected, ReSharper will prompt you choose one of the profiles.
Configure preferences for object creation expressions
Your object creation expressions' 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.
Go to the Code Editing | C# | Syntax Style page of ReSharper options (Alt+R, O).
In the Object creation category, specify whether the type specification should be preferred when the created type is evident/non-evident from usage.
The Notify with selectors in the right column allow you to set severity levels of code inspections detecting code that differs from your preferences.
Click Save in the Options dialog to apply the modifications and let ReSharper choose where to save them, or save the modifications to a specific settings layer using the Save To list. For more information, see manage and share resharper settings.
tip
Code style features that only change whitespaces, tabs, and line breaks are configurable in formatting preferences.
Applicability in different languages
This feature is supported in the following languages and technologies:
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