Enumerable "Choose" function

[Mauricio Scheffer]

Hi, I'm missing a function like F#'s Seq.choose or Haskell's catMaybes in Sasa, e.g.:

public static IEnumerable<T> Choose<T>(this IEnumerable<Option<T>> source)
{
    return source.SelectMany(x =>
    {
        T v;
        return x.TryGetValue(out v) ? new[] {v} : Enumerable.Empty<T>();
    });
}

Is this missing intentionally for some reason? Otherwise, do you think it's worth adding it to the library?

Cheers,
Mauricio

[naasking]

Not intentional, choose/catMaybe just wasn't part of the standard Linq interface. It almost seems too short to include unless it really comes up everywhere:

source.Where(x => x != null).Select(x => x.Value);

Or:

source.Where(x => x.HasValue).Select(x => x.Value);

Does it come up often enough in your programs to warrant special-casing? If so, I don't like the catMaybe name, so what's the rationale behind "choose", as opposed to some variant of "filter" or "except"? I know Seq.filter is used in F#, but unless it causes the compiler to fail, I don't think I should be beholden to that convention in Sasa.

[Mauricio Scheffer]

It really pops up everywhere in my programs, and I dislike the Value property enough to be thinking about writing an FxCop rule or something similar to disallow it :)

I can't come up with a good name for this, everything seems vague in one way or another.
I'd rule out "except" as it could be confused with Enumerable.Except ( http://msdn.microsoft.com/en-us/library/vstudio/bb300779.aspx ).
FWIW ocaml-core calls this filter_opt ( https://ocaml.janestreet.com/ocaml-core/111.28.00/doc/core_kernel/#Sequence ).

Anyway it's no big deal, I can keep this as an extension method in my code, just wondering if it was useful to be included in the library.

Cheers,
Mauricio

[Mauricio Scheffer]

Some more name ideas: WhereNotNone, WhereSome, FilterNone

[naasking]

You dislike the value property because it throws an exception when HasValue is false?

I was thinking FilterNull or ExceptNull. I was going to provide an overload for IEnumerable<t?> as well.</t?>

[Mauricio Scheffer]

Indeed, IMHO Value is an unnecessarily partial function and a case of "boolean blindness".
Good idea to apply this to IEnumerable<t?> as well, I like the name.</t?>

Cheers,
Mauricio

[naasking]

It's absolutely boolean blindness, but other than the matching function you brought up in the other thread, I don't have a better alternative for C# that can be used in all contexts, like Linq expressions.