Package gorilla/reverse is a set of utilities to create request routers.

It provides interfaces to match and extract variables from an HTTP request and build URLs for registered routes. It also has a variety of matcher implementations for all kinds of request attributes, among other utilities.

For example, the Regexp type produces reversible regular expressions that can be used to generate URLs for a regexp-based mux. To demonstrate, let's compile a simple regexp:

regexp, err := reverse.CompileRegexp(`/foo/1(\d+)3`)

Now we can call regexp.Revert() passing variables to fill the capturing groups. Because our variable is not named, we use an empty string as key for url.Values, like this:

// url is "/foo/123".
url, err := regexp.Revert(url.Values{"": {"2"}})

Non-capturing groups are ignored, but named capturing groups can be filled normally. Just set the key in url.Values:

regexp, err := reverse.CompileRegexp(`/foo/1(?P<two>\d+)3`)
if err != nil {
    panic(err)
}
// url is "/foo/123".
url, err := re.Revert(url.Values{"two": {"2"}})

There are a few limitations that can't be changed:

1. Nested capturing groups are ignored; only the outermost groups become a placeholder. So in 1(\d+([a-z]+))3 there is only one placeholder although there are two capturing groups: re.Revert(url.Values{"": {"2", "a"}}) results in "123" and not "12a3".
2. Literals inside capturing groups are ignored; the whole group becomes a placeholder.