Supporting Result and/or Choice

[jack-pappas]

For ExtCore v1.0 -- should we support both the Result<_,_> and Choice<_,_> type for error-handling, or should we drop Choice<_,_> and use only Result<_,_>?

Pros/cons of supporting Result<_,_> only:

• :+1: Smaller code size, less maintenance work (long-term)
• :+1: Just one way of doing things -- maybe simpler for less-experienced F# devs
• :-1: Result<_,_> is a struct, so doing a blanket replacement throughout code may hurt performance in cases where a Result is created wrapping a large struct and thereby induces expensive struct copies.
• :-1: Eliminating support for Choice<_,_> breaks backwards-compatibility with code written against current/past versions of ExtCore. Users of the library will have to to make non-trivial changes to their code in order to upgrade to ExtCore v1.0.

Pros/cons of supporting Result<_,_> and Choice<_,_>:

• :+1: Provides backwards-compatibility for code already written against current/past versions of ExtCore. Users should be able to (with the exception of the breaking changes defined in #47) simply upgrade to ExtCore v1.0 when it's released.
• :+1: Users can still choose between Result<_,_> and Choice<_,_> and use whatever best fits their needs.
• :-1: Adds additional complexity to ExtCore -- wherever we support error-handling within functions, we now need to implement those functions twice (once for Result, once for Choice). This is transitive as well -- any functions that call these functions also need to be implemented twice, etc.

cc @vasily-kirichenko @7sharp9 @wallymathieu @dsyme @tihan

[wallymathieu]

I've seen some non trivial code that still uses Choice, for instance Suave.

Question is how much of your own effort you want to spend (to support backwards compatibility)?

[wallymathieu]

I think that perhaps @vasily-kirichenko has the most experience using a dual Result<,> Choice<,> ExtCore. Though I remember that there was a lot of code (in that PR) in order to support that solution. For f#+ @gusty opted to start out with changing Choice<,> to Result<,> and then re-add Choice<,> based error handling with new name to support interop with libraries that still use Choice<,>.

Perhaps a compatibility method Result.OfChoice and a smaller set of combined builders could be used to limit the need for support?

[vasily-kirichenko]

@wallymathieu yes, I just pulled your PR, built a nuget package and have used it (Choice and Result are both there) on production with zero problems. So, I'm for just merge that PR.