Clawfoot.ResultPattern

A Results pattern library for .NET: return success/failure and propagate errors across layers without throwing. Use Result and Result<T> instead of exceptions for expected failure paths.

Results are immutable. Every operation returns a new instance; chain with Invoke, WithError, WithValue, or combine with Result.Combine(...).

Target: .NET Standard 2.1

Install

dotnet add package Clawfoot.ResultPattern

Quick usage

using Clawfoot.ResultPattern;

// Success (no value)
Result result = Result.Ok();
if (!result) return result;

// Success with value
Result<User> userResult = Result.Ok(user, "Found.");
if (userResult.Success)
    Console.WriteLine(userResult.Value.Name);

// Failure (immutable: each factory returns a new result)
Result err = Result.Error("Not found", userMessage: "We couldn't find that.");
Result<User> errT = Result.Error<User>("Invalid id");

Immutable patterns

Assign the returned result to keep chaining or combining:

// Add an error → new result
result = result.WithError("Validation failed");

// Combine multiple results → new result (errors combined; for Result<T>, last value wins)
Result combined = Result.Combine(result1, result2);
Result<int> combinedT = Result.Combine(r1, r2, r3);

// Chain Invoke (returns new result on exception)
result = result.Invoke(() => ValidateInput(input)).Invoke(() => SaveToDb(entity));

// InvokeResult returns Result<T>; use .Value to get the value
Result<int> r = start.InvokeResult(() => GetCount());
int value = r.Value;

Error handling in a flow

Use Invoke / InvokeAsync to run code and capture exceptions into a new result (no mutation):

var result = Result.Ok()
    .Invoke(() => ValidateInput(input))
    .Invoke(() => SaveToDb(entity));

if (!result) return result;

// Async
var result = await Result.Ok()
    .InvokeAsync(async () => await FetchAndSaveAsync());

Enum-based errors

Decorate an enum with [Error] and create results from it:

[Error(Code = 404, Message = "User not found", UserMessage = "We couldn't find that user.")]
public enum UserErrors { NotFound, InvalidId }

Result r = Result.FromError(UserErrors.NotFound);

Features

• Result and Result — immutable; Success, HasErrors, Errors, Message, Value (read-only)
• Result.Combine(...) — static method to combine multiple results (errors combined; for Result<T>, last value wins)
• WithError / WithErrors / WithException / WithValue — return a new result with added state
• Invoke / InvokeAsync / InvokeResult — wrap calls and return a new result (chainable)
• Error and IError — structured errors (Code, Message, UserMessage, GroupName); Error properties are read-only after creation
• ErrorAttribute and Error.From(enum) for enum-driven error messages
• Implicit conversion to bool (if (!result) ...)

License

LGPL-3.0-only — © 2026 Douglas Gaskell / Clawfoot Software