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Support calling default interface methods #1633

thomaslevesque opened this issue Sep 29, 2019 · 1 comment


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commented Sep 29, 2019

C# 8 introduced the "default interface methods" feature, i.e. interface methods with a default implementation (this feature works only on .NET Core 3).

Currently it's not possible with FakeItEasy to make a fake that calls the default implementation. Using CallsBaseMethods doesn't work, because Castle.Core doesn't support this feature yet (castleproject/Core#447).

We should support default interface methods in FakeItEasy.

API options:

  • Reuse CallsBaseMethods() to call the default interface methods, in addition to what it currently does.
  • Introduce a new CallsDefaultImplementation() to cover that scenario. (Maybe use a more explicit name; "default implementation" could be misleading)

Implementation options:

  • Wait for Castle.Core to support it
  • Do it ourselves. Default interface methods are methods whose declaring type is an interface and have IsAbstract == false. We need to call them non-virtually (otherwise it would cause infinite recursion). POC implementation here.

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commented Oct 1, 2019

It might be a good idea to have a separate option from CallsBaseMethods, as it gives users additional flexibility.

Alternatively, if we end up thinking that we should default to using the default interface methods, we could add FakesDefaultInterfaceMethods or similar.

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