Why Prohibit Concrete Root Values?

Grats does not allow any of the operation types, (Query, Mutation, Subscription) to have a concrete value. Instead it requires that they be defined as a type alias of unknown: type OperationType = unknown.

Fields must be declared on these types using the functional style fields syntax.

Grats forces this constraint because the semantics of the root value is not well defined across GraphQL server implementations. For example, Yoga does not allow you to define a root value, where as other server implementations use a single root value that is shared by all resolvers. Additionally, it's not specified if the root value should be shared by all requests or regenerated for each request.

There are some valid uses for a concrete root value, such as dependency injection, but in general dependency injection can be more easily achieved by using context. If you believe you have a valid use case for a concrete root value, please open an issue.