Rewrite link_checker to use a Result internally

[awonnacott]

link_checker::LinkResult always had exactly one member option set, so it should be an enum, not a struct. Instead of writing our own enum to represent sucess/failure, we can use std::result::Result.

[Keats]

What's the benefit if we are not using ??

[awonnacott]

It's not about using Result in particular, it's about how the data you are representing (EITHER code OR error) should be represented with an enum, whereas a struct "means" code AND error. If you use a struct to store two values and only one of them is set, you

• open up a class of errors which are impossible with an enum: using an uninitialized value or forgetting to check if error is set
• waste space, since your struct takes up sizeof(code) + sizeof(error) memory instead of max(sizeof(code), sizeof(error)).

Using types whose value sets correspond directly to the desired representable values is one of the big advantages of functional programming, and having well-designed enums is among the advantages Rust has over Go or C++. Consider how useful it is that existing Rust libraries return Results instead of Go-style pairs of value and error.

[Keats]

Can you cherry-pick your commit on top of next and push again?

[awonnacott]

@Keats done

[awonnacott]

hmm, tests passed on my machine, will investigate

[Keats]

Errors seem legit

[Keats]

I'll fix the error on the next branch directly; thanks!