Shared via mypy Playground

main.py

from __future__ import annotations

from dataclasses import dataclass
from typing import Protocol


# --- "generated" RPC types (pretend these come from codegen) ---

@dataclass(frozen=True)
class HelloRequest:
    name: str


@dataclass(frozen=True)
class HelloReply:
    message: str


class HelloWorldService(Protocol):
    """
    Go-style interface: any user implementation that matches this method
    signature satisfies the service contract. No inheritance required.
    """
    def SayHello(self, request: HelloRequest) -> HelloReply:
        ...


# --- framework code that "registers" the user's service implementation ---

def register_hello_world_service(service: HelloWorldService) -> None:
    # In a real RPC framework, this would store `service` in a server/router.
    # We'll just exercise it to prove both runtime + mypy behavior.
    demo_req = HelloRequest(name="Jacob")
    demo_res = service.SayHello(demo_req)
    print(f"[server] got reply: {demo_res.message}")


# --- user code: they implement the stub by matching the Protocol ---

class MyHelloWorldImpl:
    # Note: NO inheritance from HelloWorldService.
    def SayHello(self, request: str) -> HelloReply:
        return HelloReply(message=f"Hello, {request.name}!")


# --- run ---
if __name__ == "__main__":
    register_hello_world_service(MyHelloWorldImpl())