Collections

Sometimes you may find yourself working with a collection of optionals that contain the same value type, e.g. List<Option<T>>. The following methods are provided to assist you when working with collections containing optional types.

Filter

Provides the same functionality as Filter but for a collection of options. All options that do not match the provided predicate are flipped into a None.

List<Option<string>> collection = [
    Option.Some("Hello"),
    Option.Some("World"),
    Option.None<string>()
];

List<Option<string>> filtered = collection.Filter(x => x == "Hello");
//                   ^? [Option.Some("Hello"), Option.None<string>(), Option.None<string>()]

Map

Provides the same functionality as Map but for a collection of options. The same transformation will be applied to all members of the collection if they are Some.

List<Option<string>> collection = [
    Option.Some("Hello"),
    Option.Some("World"),
    Option.None<string>()
];

List<Option<string>> mapped = collection.Map(x => $"{x}!");
//                   ^? [Option.Some("Hello!"), Option.Some("World!"), Option.None<string>()]

FirstOrNone

Returns the first element of the collection that matches the predicate, or a None if there are no matches.

List<Option<string>> collection = [
    Option.Some("Hello"),
    Option.Some("World")
];

Option<string> first = collection.FirstOrNone(x => x.StartsWith("H"));
//             ^? Option.Some("Hello")

FirstOr

Returns the first element of the collection that matches the predicate, or the provided fallback value if there are no matches.

List<Option<string>> collection = [
    Option.Some("Hello"),
    Option.Some("World")
];

Option<string> first = collection.FirstOr("Victor", x => x.StartsWith("V"));
//             ^? Option.Some("Victor")

If your fallback value is expensive to generate, consider using FirstOrElse to defer execution to when a match is not found.

FirstOrElse

Returns the first element of the collection that matches the predicate, or executes the provided factory to construct the fallback value if there are no matches.

List<Option<string>> collection = [
    Option.Some("Hello"),
    Option.Some("World")
];

Option<string> first = collection.FirstOrElse(() => "Victor", x => x.StartsWith("V"));
//             ^? Option.Some("Victor")