[dan-robertson]

(1) note that “statically-typed language with generics” excludes a lot of statically typed languages, including C and Go (at least pre generics).

(2) this misses the meat of the question which is how to express that (eg) a GET request doesn’t come with a body and a POST request does. I suppose that you’re suggesting that one registers a url handler with a method type and that forces the handler to accept responses of a certain type. Or perhaps you are implicitly allowing for sun types (which aren’t a thing in many static type systems.)

(3) even in C++, isn’t this suggestion hard to work with. That is, isn’t it annoying to write a program which works for any request whether or not it has a body because the type of the body must be a template parameter that adds templates to the type of every method which is generic to it. But maybe that is ok or I just don’t understand C++.

[lkitching]

1) Looking at the TIOBE index, all the static languages I recognised on there are: C,C++,C#,Visual Basic,Go,Fortran,Swift,Delphi,Cobol,Rust,Scala,Typescript,Kotlin,Haskell and D. Of these C and Go are the only two that don't appear to support generics so I don't think this approach excludes a lot of static languages.

2) If you want to distinguish GET and POST requests statically then you just need a type for them e.g.

    GetRequest<TBody> implements Request<TBody> { }

if you don't need to do this then you can just add a method field and use a single type for both. Either way you don't need to use sum types so a language like Java can express it.

3) Yes you'll have to make functions that don't care about the body type generic so this approach could become unwieldy if you have a few such properties you want to track.