Restricting who can implement an interface

When designing an interface, it is sometimes preferable to restrict its implementation to prevent others from implementing it. This is because, once an interface is implemented, adding new members is no longer possible without breaking any class that implements it.

Metalama offers a solution to protect your interface from being implemented by other assemblies. To achieve this, follow the steps outlined below:

1. Add the Metalama.Extensions.Architecture package to your project.

2. Annotate the interface with the InternalOnlyImplementAttribute attribute. This attribute will prevent any other assemblies from implementing your interface.

Example

In the parent project, let's assume we have the following interface protected by the InternalOnlyImplementAttribute attribute:

// This is public domain Metalama sample code.

using Metalama.Extensions.Architecture.Aspects;

namespace Doc.Architecture.InternalOnlyImplement
{
    [InternalOnlyImplement]
    public interface IMyInterface { }
}

If we attempt to implement this interface in a child project, a warning is reported:

1namespace Doc.Architecture.InternalOnlyImplement
2{
    Warning LAMA0901: The 'IMyInterface' interface can only be implemented by the 'InternalOnlyImplement` project or from another project having access to its internals.

3    internal class TheImplementation : IMyInterface { }
4}