Sub router

[gsquire]

I searched through the issues but couldn't find anything for sub routers with paths. I don't care about subdomains.

My use case is for API versioning. Here is a snippet from the Gorilla mux:

r := mux.NewRouter()
s := r.PathPrefix("/products").Subrouter()
// "/products/"
s.HandleFunc("/", ProductsHandler)
// "/products/{key}/"
s.HandleFunc("/{key}/", ProductHandler)
// "/products/{key}/details"
s.HandleFunc("/{key}/details", ProductDetailsHandler)

It would be sweet to have a sub router for each version prefix. Is this currently possible or something you could add?

Forgive me if I missed something in the README or documentation.

[rickb777]

Unlike Gorilla's router, there's no performance gain from using subrouting, because the trie algorithm already handles this inherently.

So the question becomes one of how to construct formulaic paths. Although it would be a nice-to-have feature, my approach to this has been to wrap a *Router within my own path builder code instead.

[gsquire]

I'm less interested in performance than being able to unify routes based on a common path. I know how well this library performs already :)

[julienschmidt]

See #89
Working on it!

[jub0bs]

My two cents: one reason subrouters would be useful is for applying some middleware to only a subrouter.

For instance, I'd like to adapt this net/http v1.22 program to julienschmidt/httprouter, but I currently cannot because there's no way to bind a subrouter to a path without also specifying a method.

[letmestudy]

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