带有 protobuf 的嵌套枚举

Question

我正在开发一个 Rust 项目，使用 Protocol Buffers 并处理嵌套枚举。这是我迄今为止在 Rust 中所拥有的：

enum Vehicle {
    Car(CarType),
    Truck(TruckType),
}

enum CarType {
    Sedan,
    Coupe,
    Hatchback,
}

enum TruckType {
    Pickup,
    Semi,
}

fn create_vehicle_fleet() -> [Vehicle; 8] {
    [
        Vehicle::Car(CarType::Sedan),
        Vehicle::Truck(TruckType::Pickup),
        Vehicle::Car(CarType::Coupe),
        Vehicle::Truck(TruckType::Semi),
        Vehicle::Car(CarType::Hatchback),
        Vehicle::Car(CarType::Sedan),
        Vehicle::Truck(TruckType::Pickup),
        Vehicle::Car(CarType::Coupe),
    ]
}

我找不到在 protobuf 中表示车辆枚举的正确方法。任何人都可以提出解决方案或提供有关如何在 Protocol Buffers 中处理这种情况的指导吗？

Answer 1

我怀疑（！？）由于协议缓冲区的语言无关性，您不能总是直接使用原型来表示特定于语言的类型。

在这种情况下，Rust 具有强大、复杂的枚举类型，但 Protocol Buffers 只允许常量枚举。

我认为（！？）几乎相当于你需要的是：

syntax = "proto3";

// package something;

// Only messages can hold repeateds
message Foo {
    repeated Vehicle vehicles = 1;
}

// oneof permits the equivalent of a enum of non-constant types
// In some languages, the oneof name is lost but in rust it is retained
// See code snippet below
message Vehicle {
  oneof vehicle_type {
    CarType car_type = 1;
    TruckType truck_type = 2;
  }
}
// Constant enums
// If CarType|TruckType ever need fields too,
// this enum would need to be oneof
enum CarType {
  Sedan = 0;
  Coupe = 1;
  Hatchback = 2;
}
enum TruckType {
  Pickup = 0;
  Semi = 1;
}

并且，例如：

pub mod anoynmous {
    tonic::include_proto!("_");
}

use anonymous::{
    vehicle::VehicleType,
    CarType,
    Foo,
    TruckType,
    Vehicle,
};

fn main() {
    let _ = Foo {
        vehicles: vec![
            Vehicle {
                vehicle_type: Some(VehicleType::CarType(CarType::Sedan.into())),
            },
            Vehicle {
                vehicle_type: Some(VehicleType::TruckType(TruckType::Pickup.into())),
            },
        ],
    };
}