This could be achieved using a dummy validating function. const validateType = <T> (obj:T) => undefined

<ITest>foo; //a useless javascript line, but checks the var `foo` is assignable to `ITest`

If you really don't want to use any, you could use an empty interface - {} - instead:

Provides empty Module#ruby2_keywords method, for the forward source-level compatibility against ruby2.7 and ruby3.