fsetcodegen

fsetcodegen

Introduction

This is an experiment in compiling down an fset using a generator. It's a little awkward. It is also vibe coded. Yeah, I know, but I hate doing AST work and it finally made something that would work how I needed it after a few hours of tinkering.

Simple memory bound benchmarks show a 3x improvement on running:

BenchmarkFset-10 13589334 79.53 ns/op BenchmarkCompiledFset-10 61548324 19.36 ns/op

This still is multiple times longer than:

BenchmarkCallChain-10 573722551 2.073 ns/op

I'm assuming that is due to inlining, without having done much investigation.

Basically, if you do this:

//go:generate fsetcodegen -var=MyFsets

var back *exponential.Backoff

func init() {
	var err error
	back, err = exponential.New()
	if err != nil {
		panic(err)
	}
}
var MyFsets = fsets.Fset[Args]{}

func init() {
	MyFsets.Adds(fsets.C[Args]{F: Fa, B: back}, fsets.C[Args]{F: Fb}, fsets.C[Args]{F: Fc})
}

It will generate a file called fset_compiled_myfsets.go. This will contain MyFsetsCompiled(ctx context.Context, so fsets.StateObject[Args]) fsets.StateObject[Args] which is a compiled version.

If you are usng methods on a single object, it will generate constructor for you to pass that object to. This doesn't support multiple objects:

type Stuff struct{}

// ... methods

//go:generate fsetcodegen -var=MyFsets2

var MyFsets2 = &fsets.Fset[Args]{}

func init() {
	MyFsets2.Adds(
		fsets.C[Args]{F: (&Stuff{}).Fa},
		fsets.C[Args]{F: (&Stuff{}).Fb},
		fsets.C[Args]{F: (&Stuff{}).Fc},
	)
}

Will generate fset_compiled_myfsets2.go with func NewMyFsets2Compiled(ctx context.Context, obj *Stuff) func(so fsets.StateObject[Args]) fsets.StateObject[Args].

If you try to get clever with doing things like:

var MyFsets2 = (&fsets.Fset[Args]{}).Adds(fsets.C[Args]{F: (&Stuff{}).Fa})

This is going to break, this tool is just not that intelligent.

It also supports fsets inside functions. Using this syntax: //go:generate fsetcodegen -var=serveFset -func=New .

-func=New indicates the fset will be found inside the New() function.