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C# Result<TOk, TErr> type
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using System; | |
// makes sure that all references passed to this api are valid | |
// imho calls yielding nulls should actually yield err/exception if using this interface | |
#nullable enable | |
namespace Result; | |
/// <summary> | |
/// Covariant interface for <see cref="Result{TOk, TErr}"/> that assists in consumer variable binding. | |
/// <br/> | |
/// This contract implies that the interface will not throw an exception, instead allowing for happy-path error handling. | |
/// </summary> | |
/// <typeparam name="TOk">The type returned by a successful call.</typeparam> | |
/// <typeparam name="TErr">The exception type that is returned on a failed call.</typeparam> | |
public interface IResult<out TOk, out TErr> | |
where TErr : Exception | |
{ | |
interface IOk : IResult<TOk, TErr> { TOk ok { get; } } | |
interface IErr : IResult<TOk, TErr> { TErr err { get; } } | |
/// <summary> | |
/// Returns <typeparamref name="TOk"/> if bound to valid data.<br/> | |
/// Otherwise, throws <see cref="UnwrapError{TErr}"/> with the <typeparamref name="TErr"/> instance that was contained. | |
/// </summary> | |
/// <exception cref="UnwrapError{TErr}"/> | |
TOk Unwrap(); | |
/// <summary> | |
/// Returns <typeparamref name="TOk"/> if bound to valid data.<br/> | |
/// Otherwise, returns <see langword="default"/> of <typeparamref name="TOk"/>. | |
/// </summary> | |
TOk? UnwrapOrDefault(); | |
/// <summary> | |
/// <c><see langword="true"/> if <see langword="this"/> is <see cref="Result{TOk, TErr}.Err"/> else <see langword="false"/></c> | |
/// </summary> | |
bool IsOk(); | |
/// <summary> | |
/// <c><see langword="true"/> if <see langword="this"/> is <see cref="Result{TOk, TErr}.Ok"/> else <see langword="false"/></c> | |
/// </summary> | |
bool IsErr(); | |
} | |
/// <summary> | |
/// The exception that is thrown when <see cref="Result{TOk, TErr}.Unwrap"/> is called on an instance that wraps an error instead of valid data. | |
/// </summary> | |
/// <param name="InnerException">The <typeparamref name="TErr"/> that was actually contained by the <see cref="Result{TOk, TErr}"/> instance.</param> | |
public class UnwrapError<TErr>(TErr innerException) | |
: Exception("Tried to unwrap an error", innerException) | |
where TErr : Exception | |
{ | |
public TErr Exception { get; } = innerException; | |
} | |
/// <summary> | |
/// An object that contains either <typeparamref name="TOk"/> or <typeparamref name="TErr"/>, depending on the outcome of a method call. | |
/// </summary> | |
/// <typeparam name="TOk"/> | |
/// <typeparam name="TErr"/> | |
public record Result<TOk, TErr> : IResult<TOk, TErr> | |
where TErr : Exception | |
{ | |
public record Ok(TOk ok) : Result<TOk, TErr>, IResult<TOk, TErr>.IOk { } | |
public record Err(TErr err) : Result<TOk, TErr>, IResult<TOk, TErr>.IErr { } | |
public static implicit operator Result<TOk, TErr>(TOk ok) => new Ok(ok); | |
public static implicit operator Result<TOk, TErr>(TErr err) | |
{ | |
if (err.StackTrace is null) | |
try { throw err; } catch { } // not pretty, but should preserve the stack trace if converted from an unthrown exception instance | |
return new Err(err); | |
} | |
/// <inheritdoc/> | |
public TOk Unwrap() => | |
this switch | |
{ | |
Ok ok => ok.ok, | |
Err err => throw new UnwrapError<TErr>(err.err), | |
_ => throw new Exception("never") | |
}; | |
/// <inheritdoc/> | |
public TOk? UnwrapOrDefault() => | |
this switch | |
{ | |
Ok ok => ok.ok, | |
_ => default | |
}; | |
/// <inheritdoc/> | |
public bool IsErr() => this is Err; | |
/// <inheritdoc/> | |
public bool IsOk() => this is Ok; | |
} |
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