The Result Pattern in .NET

Start by defining the Error and Result models

// Error.cs
public record Error(string Code, string Message);

// Result.cs
public class Result<T> : Result
{
    [JsonPropertyName("data")]
    [JsonPropertyOrder(2)]
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
    public T Value { get; }

    [JsonConstructor]
    private Result(int statusCode, bool isSuccess, T value, Error error) : base(statusCode, isSuccess, error)
    {
        StatusCode = statusCode;
        Value = value;
    }

    public static Result<T> Success(T value, int statusCode = 200) =>
        new(statusCode, true, value, null!);
    public new static Result<T> Failure(int statusCode, Error error) =>
        new(statusCode, false, default!, error);
}

public class Result
{
    [JsonPropertyName("status_code")]
    [JsonPropertyOrder(1)]
    public int StatusCode { get; set; }

    [JsonPropertyName("success")]
    [JsonPropertyOrder(0)]
    public bool IsSuccess { get; }

    [JsonIgnore(Condition = JsonIgnoreCondition.Always)]
    public bool IsFailure => !IsSuccess;

    [JsonPropertyOrder(3)]
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
    public Error Error { get; }

    [JsonConstructor]
    protected Result(int statusCode, bool isSuccess, Error error)
    {
        StatusCode = statusCode;
        IsSuccess = isSuccess;
        Error = error;
    }

    public static Result Success(int statusCode = 200) =>
        new(statusCode, true, null!);
    public static Result Failure(int statusCode, Error error) => new(statusCode, false, error);
}

Note that the generic result type Result<T> is only required if you want to return data

Define static Error classes based on your application needs. For example:

public static class UserErrors
{
   public static Error NotFound =>
       new("NOT_FOUND", "The requested user was not found.");
    public static Error ProfileUpdateFailed =>
       new("PROFILE_UPDATE_FAILED", "Failed to update user profile. Please try again later.");
}

Then use your newly found superpowers like so

if (user is null)
{
       logger.LogWarning("User not found for changing password: {UserId}", userId);
       return Result.Failure(UserErrors.NotFound);
}
// ...
logger.LogInformation("Password changed successfully for user ID: {UserId}", userId);
return Result.Success();

If you would like to return additional data, then…

return Result<UserProfileDto>.Success(user);

I'd take this over exceptions for flow-control any day. Exceptions have their place; this is not it.