Result

Description

Result represents the result of an operation. If the operation fails, Result will contain the exception that occurred; otherwise, Result will contain the value resulting from the operation.

The method responsible for the operation must return a Result with the value resulting from the operation, or in case of failure, it must return a Result with an exception. The consumer code must extract the result through one of the available methods.

The result of the operation can be extracted through several methods such as: Match(), ValueOrDefault, CaseSuccess(), CaseFailure(), IsSuccess() and IsFailure().

Note that no exceptions are thrown. Exceptions are just created and returned to the calling code which must decide what to do with them.

Use

Example of a method responsible for the validation operation.

public static Result<string> TryValidate(string? s, IFormatProvider? provider = default)
{
    if (s is null)
        return new Result<string>(new ArgumentNullException(nameof(s)));

    if (s.Length > MaxLength)
        return new Result<string>(new ArgumentException(
            message: $"{nameof(Name)} is invalid. The value '{s}' must be at most {MaxLength} characters and currently has {s.Length} characters.",
            paramName: nameof(s)));

    return new Result<string>(s);
}

Example of two methods that use Result.

public static Result<Name> TryParse(string? s, IFormatProvider? provider = default) =>
    TryValidate(s, provider).Match(
        Success: x => new Result<Name>(new Name(x)),
        Failure: e => new Result<Name>(e));

public static bool IsValid(string? s, IFormatProvider? provider = null) =>
    TryValidate(s, provider).Match(
        Success: x => true,
        Failure: e => false);

Public Methods

Match

R Match<R>(Func<T, R> Success, Func<Exception, R> Failure)

If it is a successful result, it returns the value of the Success function, 
otherwise it returns the value of the Failure function.

Match(Action<T> Success, Action<Exception> Failure)

If it is a successful result, it executes the Success action, otherwise it executes the Failure action.

CaseSuccess

R CaseSuccess<R>(Func<T, R> Success, Func<Exception, R> defaultValue)

If it is a successful result, it returns the value of the Success function, 
otherwise it returns the value of the defaultValue function.

bool CaseSuccess(Action<T> Success)

If it is a successful result, it executes the Success action, otherwise it returns false.

ValueOrDefault

T ValueOrDefault(Func<Exception, T> Failure) => Match(value => value, Failure)

If it is a successful result, it returns the value of the result, otherwise it returns the value of the Failure function.

CaseFailure

bool CaseFailure(Action<Exception> Failure)

If it is a failure result, it executes the Failure action and return true, otherwise it returns false.

IsSuccess

bool IsSuccess()

If it is a successful result, it returns true, otherwise it returns false.

IsFailure

bool IsFailure()

If it is a failure result, it returns true, otherwise it returns false.

References

C# functional language extensions - louthy/language-ext

Don't throw exceptions in C#. Do this instead - Nick Chapsas