Gen on builtin types

[james-m]

Hello,

Sorry if this question is answered somewhere in the docs / another issue, I was unable to find if this is currently possible.

Basically, I would like generate slices on builtin types... I'm working around it by creating type which are just aliases of the builtin, then going into the generated code and doing a find-and-replace of the function params/return values. Blek!

So, for example, I have this:

//+gen set
type String string

I run gen, which creates the string_set.go file, which I then go in and change String back to string (where it makes sense).

Any thoughts? Thanks very much.

[clipperhouse]

I don’t know a good way to do this (have wanted for myself too). Aliasing is the “supported” way – gen’s supported use case is for local (package) types only.

The issue is, how does one add a gen directive (comment) to a built-in type? I think this might be better implemented as a whole separate package – “genp” for primitives, or something.

[hieuht817]

I would love it can gen on any types: built-in, 3rd-party, local...
Why does it need coupling the directive with the type's source code?

[artwyman]

This is an awkward workaround, but could you avoid this with a custom TypeWriter which ignored its primary Type and just took all of its type parameters from tag values? e.g.

// +gen myset:"ValueType[string]"
type DummyType struct{}

This is awkward in that the myset typewriter would need to duplicate what "set" already does except with different paramters, and also because DummyType only exists as a place to attach an annotation.

FWIW I think gen is awesome, but this limitation is pushing me away from it as a solution vs. other alternative generators out there. I'd like to support generators on primitive types (like generating min/max functions), and generators which need multiple parameters (like TreeMap<K,V>). The workaround here seems too awkward for me to want to sell to other developers. It would be nice if gen could support this directly with a direct way to specify the "primary type" in an annotation without being attached to it, such as what was suggested in #99.

[clipperhouse]

@artwyman Thanks for using gen! It does parse multiple type parameters, and they are exposed on TagValue.

Yeah, my biggest blocker for primitive types is the notation — there is no type declaration to mark up. I like the markup to be in the repo, near the type. Easily understandable, self-documenting.

I’m not a huge fan of command-line args though I suppose it’s not the end of the world. It means that definitions (potentially) live outside the repo, and far from the type, and it’s a little harder to give good feedback on errors.