Result Type

Result<T> is similar to std::result data type in Rust programming language and allows to handle method call errors without try-catch block. The value can contain actual result returned from method or error in the form of exception.

.NET library provides TryInvoke extension methods to return Result<T> from popular delegate types such as Func, Converter. The type behaves like monad and the pipeline of calls can be constructed.

using DotNext;

Func<string, int> parser = int.Parse;
Result<int> result = parser.TryInvoke("42");
if (result)  //successful
{
    var i = (int)result;
}
else
{
    throw result.Error;
}

This type is paired with Optional data type. Result<T> can be converted to it implicitly. But conversion loses information about exception:

using DotNext;

Func<string, int> parser = int.Parse;
int result = parser.TryInvoke("42").OrInvoke(static error => 0);

Custom error codes

Result<T, TError> is an overloaded type that allows to use custom error codes instead of exceptions. The second generic parameter expects enum type that enumerates all possible error codes.

using DotNext;

enum ErrorCode
{
    Success = 0,
    InvalidInputString,
}

static Result<int, ErrorCode> TryParse(string input) => int.TryParse(input) ? input : new(ErrorCode.InvalidInputString);

Both types are interoperable:

Result<int, ErrorCode> result1 = TryParse("123");
Result<int> result2 = result1;