ValueOr and AsMaybe for results

[RorySan]

Hello, I wrote two simple extension methods that are helping me in my project, but I'm guessing there is probably a better alternative already built in that I am not using:

    public static Maybe<T> AsMaybe<T>(this Result<T> result) =>
        result.IsSuccess ? result.Value : Maybe<T>.None;
    
    public static string ValueOr<T>(this Maybe<T> maybe, string alternativeValue) 
        where T : SimpleValueObject<string> => 
        maybe.HasValue ? maybe.Value : alternativeValue;

I found a way of using the existing Or to achieve this, but it is a bit more verbose. With this ValueOr i get to write things like Email.ValueOr(string.Empty) which is handy when displaying optional info on the UI. Am I missing a better way of doing this?

[bothzoli]

Hey @RorySan,

There's a GetValueOrDefault method defined on Maybe that you could use instead of your ValueOr.

public T GetValueOrDefault(T defaultValue)
{
    if (HasNoValue)
        return defaultValue;

    return _value;
}

For the AsMaybe I did not find anything that would do the same thing, but I may be wrong.
It sounds like a useful enough method.
@vkhorikov or @hankovich do you if there's such a conversion from Result to Maybe and if not, why not?
Would it make sense to include that?

[RorySan]

Thanks for your reply @bothzoli , although I think GetValueOrDefault wouldn't work in this case because I am not returning T but string. I'll get back to you with the detailed use case and we can decide if it might make sense to include it.

I've been exploring functional programming for a while now and I use this library extensively. I'm not very experienced with contributions, but I'd be happy to help if that's ok.

[bothzoli]

In the extension method you sent above, the generic type constraint makes T a SimpleValueObject<string>, which in turn makes the T of the public T Value of the value inside the Maybe a string.
This sounds a bit confusing, but the point is, I believe you could as well use a Maybe<string> instead of the Maybe<SimpleValueObject<string>>.
In that case the T returned by GetValueOrDefault will actually be a string, as you need it to be.

This all however makes me wonder what you use the ValueOr method for? This method would "unwrap" the Maybe. Why not just Map over it?

[vkhorikov]

2. For ValueOr, there's an Or extension that accepts Maybe and returns Maybe, and there's also GetValueOrDefault that accepts T and returns T

GetValueOrDefault wouldn't work in this case because I am not returning T but string

You can do a Map before, as in:

Maybe<MyValueObject> myMaybe = ...
myMaybe
    .Map(x => x.Value) // Maybe<string>
    .GetValueOrDefault(string.Empty) // string

1. I don't think we have an AsMaybe that works on top of Result, we can add one.

[RorySan]

I see @vkhorikov . I'll tinker a bit with my use case and let you know. Your solution seems right, although I think it made sense for me to have a custom method for brevity given I use it a lot on my UI. That does not justify adding it to the library tho.

Regarding the AsMaybe for Result, shall I prepare a PR with the functionality and tests and send it your way? Seems small enough for a first timer 😅. Is there anything special I should take into account? Thanks!

[vkhorikov]

Yep, feel free to submit a PR please

[RorySan]

I've sent the PR. I'm not experienced at all in these matters, this is my first PR to an open source project. If I'm doing something wrong or not following best practices, please do not hesitate to point it out. Thanks.

[bothzoli]

Adding PR reference #597.
I was only able to skim through it and so far it looks good.
I wonder if it'd make sense to add the extension method to the other result class variants (UnitResult, Result<T,E>)?
What do you think @vkhorikov?