Typically, you'll want to keep Global Usings in a single location.

[MNF]

It will be useful to provide further tip, which single location is recommended .
Do you recommend it be in the top of Program.cs (if such file exists in the project)?
Or create some file GlobalUsings.cs in Properties subfolder?
Or something else?

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Document Details

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• ID: 7569e51d-92c7-294a-2d5f-e1ab3c35fdf8
• Version Independent ID: 86a1c11a-1d3c-902b-6cf3-5c004c59a856
• Content: using directive - C# Reference
• Content Source: docs/csharp/language-reference/keywords/using-directive.md
• Product: dotnet-csharp
• Technology: csharp-language-reference
• GitHub Login: @BillWagner
• Microsoft Alias: wiwagn

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Associated WorkItem - 343931

[sharwell]

The SDK creates a generated file with global using directives defined via the project. The approach I recommend for adding to this list is adding new global using items to the project file itself, and these will be added to the same location.

[BillWagner]

I'm adding this to our backlog, and adding the "discussion" label.

@CyrusNajmabadi @jinujoseph Do we have analyzers that make a recommendation for where global usings should be added in a project?

[ahaleiii]

I'm experimenting with Program.Usings.cs, which can be nested under Program.cs if desired.

I would prefer to keep global usings out of Program.cs so that top level programs can stay small and on point.

[Bunnywood]

A separate file is a cleaner solution in my opinion, fwiw :)

[sharwell]

I'm adding this to our backlog, and adding the "discussion" label.

@CyrusNajmabadi @jinujoseph Do we have analyzers that make a recommendation for where global usings should be added in a project?

We don't have any refactorings right now, but we did discuss the desired placement.
dotnet/roslyn#55895 (comment)

The primary desired placement is likely to be the project file, as this location has already been adopted by the .NET SDK.

[peteraritchie]

The primary desired placement is likely to be the project file, as this location has already been adopted by the .NET SDK.

Is this issue about global usings in general (i.e. both "explicit" and implicit) or "explicit" (i.e. advice on C# using directives)? I can see the value in having advice for both. e.g.:

DO prefer implicit global usings
DO place global using directives in program.cs

Correct me if I'm wrong; the C# using directive does not apply to a .csproj file.

[peteraritchie]

from https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-10:

You can add the global modifier to any using directive to instruct the compiler that the directive applies to all source files in the compilation. This is typically all source files in a project.

"Typically": when does it not apply to all files in a project?

[peteraritchie]

For me, things at the same scope should either exist in the same place or be isolated to the same extent.

I try to avoid introducing coupling in more than one dimension at a time (i.e. introducing coupling for disparate reasons). For example, a.cs and b.cs may be coupled together by existing in the same project, but they are loosely coupled with one another otherwise (e.g., there's no content coupling; b.cs is not coupled to anything within a.cs, and vice versa).

If global usings were added neither to a.cs nor b.cs, their degree of isolation would be maintained. But, if I put a global using in a.cs such that b.cs is compile-time (i.e. content coupling) dependent on a.cs, that looseness is diminished.