Feature: Extensions for IEnumerable<Maybe<T>>

I was wondering if there was any value in extensions like these:

public static IEnumerable<T> MapValues<T, K>(this IEnumerable<Maybe<T>> maybes) =>
    maybes.Where(m => m.HasValue).Select(m => m.Value);

public static IEnumerable<K> MapValues<T, K>(this IEnumerable<Maybe<T>> maybes, Func<T, K> selector) =>
    maybes.Where(m => m.HasValue).Select(m => selector(m.Value));

I do run into situations where I have a collection of Maybe<T> and I want to filter to only the items in the collection that have a value and then map that value.

Currently, I use the implementation maybes.Where(m => m.HasValue).Select(m => m.Value), and even though there’s no other way to do it, I’d prefer not to see it in my code 😃

I’m not sold on the name .MapValues(), but I’m not sure what would be appropriate.

[vkhorikov]

Yeah, I use maybes.Where().Select() a lot too. A new extension method wouldn’t hurt. Regarding naming, FilterValues would probably be better. The method contains both filtration (Where) and mapping (Select), but I think the emphasis here should be on filtration, the mapping part is going to be obvious from the signature. I’m open for other suggestions too, though.

[vkhorikov]

I didn’t know about Choose in F#, but now that I read about it, it makes sense. Just for future reference, here’s the difference between choose and filter:

List.choose : ('T -> 'U option) -> 'T list -> 'U list
List.filter : ('T -> bool) -> 'T list -> 'T list

Let’s keep Choose. We’ve already gone the F# way when we separated different OnSuccess overloads into Map and Bind, so I prefer to stick to the F# style for consistency.

@seangwright Regarding the documentation, I’ve been planning to do it for a long time, but currently my priority is the new course, I hope to work on the documentation once I finish it. Your readme updates look good, feel free to submit a PR, I’ll merge them. I also plan to do a separate website with the docs, similar to FluentValidation ( https://fluentvalidation.net/ ), the readme file will be the backbone for that future docs website.

Edit: I see that you already submitted a PR, looking into at.