consider using generics to aid the constructor magic

[marten-seemann]

I think the design makes sense. My only worry as a user is that opts ...interface{} is very unsafe at a static level, but I don't think you can do any better without generics. Once you had generics, you could do funky stuff like:

package libp2p

type constructor[T any] func() *T

type option[T any] func(*T)

func Transport[T any, TConstructor constructor[T], TOption option[T]] func(ct TConstructor, opts ...TOption) Option

Note that this would not support arbitrary parameters before the variadic options, like the upgrader in func NewTCPTransport(upgrader *tptu.Upgrader, opts ...Option). I don't think 1.18 generics has support for "arbitrary parameters" like that. But perhaps those could be redesigned to fit generics, to perhaps even remove the need for reflection.

Very much getting off-topic here. Just food for thought, in case you considered generics :)

Originally posted by @mvdan in #1205 (review)