Add validation warning for `sealed` classes containing benchmarks

[JeppeSN]

It is easy to create benchmarks, for example as shown in README.md:

// attributes here
public class Md5VsSha256
{
  // setups and benchmarks here
}

However, if I choose to seal my class, as in:

public sealed class Md5VsSha256

then if I use BenchmarkSwitcher.FromAssemblies(...).Run(...) to run my benchmarks, then the class is no longer discovered.

Is there any technical reason for this behavior?

It seems that if you go to src/BenchmarkDotNet/Extensions/ReflectionExtensions.cs line 159 and remove the .IsSealed criterion, then this should work?

In the project I am working in, we prefer to make all types sealed unless they are specifically designed to be base classes, and this practice improves performance in general, so it is a shame if classes containing benchmarks cannot also be sealed.

[timcassell]

Is there any technical reason for this behavior?

Your benchmark class cannot be sealed because BDN generates a class that inherits it in order to actually run the benchmarks. https://github.com/dotnet/BenchmarkDotNet/blob/e6fdc6b3c4d540983641f5aeca9c93308dc0da7a/src/BenchmarkDotNet/Templates/BenchmarkType.txt#L2

[timcassell]

Perhaps it would be better to display a warning rather than ignore it silently.

[JeppeSN]

@timcassell, All right, my question was based on general ignorance, and this is clearly much more complex than I had imagined.

There are likely a variety of different ways BenchmarkDotNet could be used. In our use, it seems the template was not used. But then I did not actually have the attribute [SimpleJob] on my class (called Md5VsSha256 in the example).

After having seen the template Templates/BenchmarkType.txt, if I do include [SimpleJob], and also introduce an evil member like:

public int BenchmarkDotNet { get; set; }

to make sure the code in the template will not compile, I do see output indicating the compile-time error, so I can see that a template is used then. However (removing the evil BenchmarkDotNet property), if I make a check in the constructor:

public Md5VsSha256()
{
    if (GetType() != typeof(Md5VsSha256))
    {
        throw new InvalidOperationException("See, template type is instantiated.");
    }
}

then I do not see any indication that the line 6 from the template, BenchmarkDotNet.Autogenerated.Runnable_$ID$ instance = new BenchmarkDotNet.Autogenerated.Runnable_$ID$(); // do NOT change name "instance" (used in SmartParamameter), is run, in my use.

Anyway, this is probably not worth pursuing further. Thank you for your answer.

[adamsitnik]

We should reconsider writing the code analyzers for BDN, similar to what xUnit provides.