Go是否支持函数的类型转换/转换？

Question

I am writing a library named "GoRequest" which wraps around net/http package and is meant for making an easy http client.

Now, I am having a problem with function conversion which has similar types as its parameters. Here is my problem snippet.

type Request *http.Request
type Response *http.Response

func (s *SuperAgent) RedirectPolicy(policy func(req Request, via []Request) error) *SuperAgent {
   s.Client.CheckRedirect = policy
   return s
}

s.Client.CheckRedirect is a member in http.Client struct and should receive func(req *http.Request, via []*http.Request) error

As you might see, I want to convert func(req Request, via []Request) error --> func(req *http.Request, via []*http.Request) which has similar types of parameters.

But it returns me an error:

./main.go:142: cannot use policy (type func(Request, []Request) error) as type func(*http.Request, []*http.Request) error in assignment

I cannot find any document for this kind of conversion and if it's possible, please suggest. If not, please suggest some other good way to do this. Thanks!

Answer 1

Can't you just wrap policy in an anonymous function that would do the conversion for you? Something like this:

func (s *SuperAgent) RedirectPolicy(policy func(req Request, via []Request) error) *SuperAgent {
   s.Client.CheckRedirect = func(r *http.Request, v []*http.Request) error {
       return policy(Request(r), []Request(v))
   }
   return s
}

I'm not actually sure you can convert the []*http.Request slice to a []Request, but if not, you could create a temporary slice and do the interface conversion one by one:

func (s *SuperAgent) RedirectPolicy(policy func(req Request, via []Request) error) *SuperAgent {
   s.Client.CheckRedirect = func(r *http.Request, v []*http.Request) error {
       vv := make([]Request, len(v))
       for i, r := range v {
           vv[i] = Request(r)
       }
       return policy(Request(r), vv)
   }
   return s
}

That should do it.