Visual Studio Warning – Prefix 'S_' or 'T_' is not expected

Whenever I create many constants for different purposes in a project, I tend to categorize them by putting a one letter prefix and an underscore in front of the names. Now, I chose the prefix T_ for some constants and noticed that the compiler gave me a warning:

IDE1006: Naming rule violation: Prefix 'T_' is not expected

That made me really curious, since I have no naming rule configured that says anything about that prefix, so I experimented a little. This warning only shows for the letters S and T, both uppercase and lowercase, so other prefixes like A_, b_ or Z_ are allowed. I tried this with local variables, properties, constants, methods and classes, and for all those cases, this rule applies: No uppercase or lowercase T_ or S_ at the start of an identifier. I know there are many cases I didn’t test, but I’m pretty sure this is consistent across all sorts of identifiers in C#.

Now the question is, why is that? Are the prefixes T_, t_, S_, s_ used for anything specific internally, or is it a general naming convention that I simply don’t know anything about?

I already googled for the specific message about the prefix, or the prefix in general, and I also took a very brief look at the documentation of IDE1006. None of those things yielded any answers.

Since it was requested, here’s my .editorconfig:

[*.cs]

# IDE0039: Use local function
dotnet_diagnostic.IDE0039.severity = silent

As you can see, there is nothing naming related here.

And here’s my .csproj:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

PS: I know using underscores in identifiers is sort of frowned upon, the reason I use them is because I name my constants in capslock, which, I think, is also frowned upon? I do that because I prefer having a clear indication of what’s a constant and what isn’t.

>Solution :

Are the prefixes T_, t_, S_, s_ used for anything specific

Quote the coding conventions manual:

When working with static fields that are private or internal, use the s_ prefix and for thread static use t_.

public class DataService
{
   private static IWorkerQueue s_workerQueue;

   [ThreadStatic]
   private static TimeSpan t_timeSpan;
}