Result types

Result

Result is a built-in generic type that either holds a Success value or a Failure value, where Success and Failure are type parameters.

You can construct a result inline, without giving it a name, usually to specify the return type of an operation. For example:

module VisitorCenter

interface Greeter {
    greet(name: string) -> Result<string, GreeterError>
}

/// The errors returned by the Greeter.
unchecked enum GreeterError {
    EmptyName
    NameTooLong(maxLength: int32)
    Away(until: WellKnownTypes::TimeStamp)
}

You can also use a constructed result as the type of a field, the element type of a sequence, the type of an operation parameter, and so on, just like any other Slice type.

A result is conceptually equivalent to a compact variant enum with two variants (Success and Failure), each with a single field of the associated type. You can see Result<string, GreeterError> as a convenient way to reference:

compact enum Result<string, GreeterError> { // not a valid Slice identifier
    Success(value: string)
    Failure(value: GreeterError)
}

C# mapping

Result<Success, Failure> maps to Result<TSuccess, TFailure>, where Result<TSuccess, TFailure> is a C# record class in the ZeroC.Slice namespace.

The Slice type parameters are mapped to C# type parameters, following the usual mapping rules. For example:

The C# Result record class is a discriminated union with a number of helper methods provided by Dunet.

For example, you can process the Result<string, GreeterError> shown earlier with the following code:

// Match and MatchAway are methods generated Dunet.
string message = result.Match(
    success => success.Value,
    failure => failure.Value.MatchAway(
        away => $"Away until {away.Until.ToLocalTime()}",
        () => $"{failure.Value}"));