language-ext v3.3.43 Release Notes

Release Date: 2019-12-10 // almost 3 years ago
  • 0️⃣ Language-ext was created before the C# pattern-matching feature existed. The default way to match within lang-ext is to use the Match(...) methods provided for most types.

    👍 There have been requests for the struct types to become reference-types so sub-types can represent the cases of types like Option<A>, Either<L, R>, etc. I don't think this is the best way forward for a number of reasons that I won't go in to here, but it would obviously be good to support the C# in-built pattern-matching.

    So, now most types have a Case property, or in the case of delegate types like Try<A>, or in-built BCL types like Task<T>: a Case() extension method.

    For example, this is how to match on an Option<int>:

    var option = Some(123);var result = option.Case switch{ SomeCase\<int\>(var x) =\> x, \_=\> 0// None};
    

    Next we can try matching on an Either<string, int>:

    var either = Right\<string, int\>(123);var result = either.Case switch{ RightCase\<string, int\>(var r) =\> r, LeftCase\<string, int\>(var \_) =\> 0, \_=\> 0// Bottom};
    

    This is where some of the issues of C#'s pattern-matching show up, they can get quite verbose compared to calling the Match method.

    For async types you simply have to await the Case:

    var either = RightAsync\<string, int\>(123);var result = await either.Case switch{ RightCase\<string, int\>(var r) =\> r, LeftCase\<string, int\>(var \_) =\> 0, \_=\> 0// Bottom};
    

    The delegate types need to use Case() rather than Case:

    var tryOption = TryOption\<int\>(123);var result = tryOption.Case() switch{ SuccCase\<int\>(var r) =\> r, FailCase\<int\>(var \_) =\> 0, \_=\> 0// None};
    

    👍 All collection types support Case also, they all work with the same matching system and so the cases are always the same for all collection types:

    static int Sum(Seq\<int\> seq) =\>seq.Case switch { HeadCase\<int\>(var x) =\> x, HeadTailCase\<int\>(var x, var xs) =\> x + Sum(xs), \_=\> 0// Empty };