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CA1812: Avoid uninstantiated internal classes

  • Artikkeli
Property Value
Rule ID CA1812
Title Avoid uninstantiated internal classes
Category Performance
Fix is breaking or non-breaking Non-breaking
Enabled by default in .NET 9 No

Cause

An internal (assembly-level) type is never instantiated.

Rule description

This rule tries to locate a call to one of the constructors of the type and reports a violation if no call is found.

The following types are not examined by this rule:

  • Value types
  • Abstract types
  • Enumerations
  • Delegates
  • Compiler-emitted array types
  • Types that can't be instantiated and that only define static methods.

If you apply System.Runtime.CompilerServices.InternalsVisibleToAttribute to the assembly that's being analyzed, this rule doesn't flag types that are marked as internal (Friend in Visual Basic) by default, because a field may be used by a friend assembly. To analyze the assembly anyway, see Configure code to analyze.

How to fix violations

To fix a violation of this rule, remove the type or add code that uses it. If the type contains only static methods, add the static modifier to the type to prevent the compiler from emitting a default public instance constructor.

When to suppress warnings

It is safe to suppress a warning from this rule. We recommend that you suppress this warning in the following situations:

  • The class is created through late-bound reflection methods such as System.Activator.CreateInstance.

  • The class is registered in an inversion of control (IoC) container as part of the dependency injection pattern.

  • The class is created automatically by the runtime or ASP.NET. Some examples of automatically created classes are those that implement System.Configuration.IConfigurationSectionHandler or System.Web.IHttpHandler.

  • The class is used as a type parameter in a class definition and has a new constraint. The following example will be flagged by rule CA1812:

    internal class MyClass
{
    public void DoSomething()
    {
    }
}
public class MyGeneric<T> where T : new()
{
    public T Create()
    {
        return new T();
    }
}

MyGeneric<MyClass> mc = new MyGeneric<MyClass>();
mc.Create();

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1812
// The code that's violating the rule is on this line.
#pragma warning restore CA1812

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1812.severity = none

For more information, see How to suppress code analysis warnings.

Configure code to analyze

Use the following option to configure which parts of your codebase to run this rule on.

You can configure this option for just this rule, for all rules it applies to, or for all rules in this category (Performance) that it applies to. For more information, see Code quality rule configuration options.

Ignore InternalsVisibleTo attribute

By default, this rule is disabled if the assembly being analyzed uses InternalsVisibleToAttribute to expose its internal symbols. To specify that the rule should run even if the assembly is marked with InternalsVisibleToAttribute, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.ignore_internalsvisibleto = true

This option is available starting in .NET 8.