Optional enum values with proto3

[Eugene Zhoga]

Hi,

Is it possible to wrap somehow enum (like primitive type) to have Option[EnumType] as output (proto3 is used)?

The only possibility for now I see is to wrap it into message but in this case it looks a bit ugly, like value = Some(EnumWrapper(EnumValue))

Is it any technic how to eliminate this intermediate EnumWrapper?

Thank you.

Evgeny

[Nadav Samet]

There isn't a generic way to do it. One option to consider would be to use Int32Value from wrappers.proto (https://scalapb.github.io/customizations.html#primitive-wrappers) and add a custom type that would convert between Int32Value and the enum (https://scalapb.github.io/customizations.html#custom-types).

You can also use your own message type (MyEnumValue) and use a type mapper to convert between MyEnumValue and the value that is inside, but that requires a message type for each enum. It's probably the preferred way because this is more type-safe for non-ScalaPB users (the proto would reference the enum type and not just an int32)

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-Nadav

[Eugene Zhoga]

@Nadav Samet: Once again, thank you!

To extend your reply with some code snippets (to cover both cases + mapping to string):

proto description

syntax = "proto3";

option java_package = "com.example";

import "google/protobuf/wrappers.proto";
import "scalapb/scalapb.proto";

option (scalapb.options) = {
    import: "com.example.Converters._"
};

enum Error {
    NoError = 0;

    SomeEnumError = 999999;
}
message EnumsHolder {
    enum SomeEnum {
        SomeValue = 0;

        reserved 999999; // error mapping
    }
    message SomeEnumWrapper {
        SomeEnum value = 1;
    }
}

message OptionalEnumUsage {
    int32 id = 1;
    EnumsHolder.SomeEnumWrapper enum1 = 2 [(scalapb.field).type="EnumsHolder.SomeEnum"];
    google.protobuf.Int32Value enum2 = 3 [(scalapb.field).type="EnumsHolder.SomeEnum"];
    google.protobuf.StringValue enum3 = 4 [(scalapb.field).type="EnumsHolder.SomeEnum"];
}

and Converters:

package com.example

import com.google.protobuf.wrappers.{Int32Value, StringValue}
import scalapb.TypeMapper

object Converters {
  implicit val Int32Value2NezasaTouroperatorMapper: TypeMapper[Int32Value, EnumsHolder.SomeEnum] =
    TypeMapper[Int32Value, EnumsHolder.SomeEnum](i => EnumsHolder.SomeEnum.fromValue(i.value))(e => Int32Value(e.value))

  implicit val StringValue2NezasaTouroperatorMapper: TypeMapper[StringValue, EnumsHolder.SomeEnum] =
    TypeMapper[StringValue, EnumsHolder.SomeEnum](i => EnumsHolder.SomeEnum.fromName(i.value).getOrElse(EnumsHolder.SomeEnum.Unrecognized(Error.SomeEnumError.value)))(e => StringValue(e.name))

  implicit val SomeEnumWrapper2SomeEnumMapper: TypeMapper[EnumsHolder.SomeEnumWrapper, EnumsHolder.SomeEnum] =
    TypeMapper[EnumsHolder.SomeEnumWrapper, EnumsHolder.SomeEnum](_.value)(EnumsHolder.SomeEnumWrapper().withValue)

}

Best regards,

Evgeny