add request Scopes api, the user can add parameters dynamically.

request.go

@@ -604,6 +604,28 @@ func (r *Request) AddRetryCondition(condition RetryConditionFunc) *Request {
 	return r
 }
 
+// Scopes pass current request instance to arguments `func(*Request) *Request`,
+// which could be used to add parameters dynamically
+//     func TransferContentType(r *Request) *Request {
+//          return r.SetHeader("Content-Type", "application/json").
+//              SetHeader("Accept", "application/json")
+//     }
+//
+//     func PageParam(page, size int) func (r *Request) *Request  {
+//         return func(r *Request) *Request {
+//             return r.SetQueryParam("page", strconv.FormatInt(int64(page), 10)).
+//                  SetQueryParam("size", strconv.FormatInt(int64(size), 10))
+//         }
+//     }
+//
+//     r.Scopes(TransferContentType, PageParam(1, 100)).Get("https://localhost:8080/bar")
+func (r *Request) Scopes(funcs ...func(r *Request) *Request) *Request {
+	for _, f := range funcs {
+		r = f(r)
+	}
+	return r
+}
+
 //‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
 // HTTP request tracing
 //_______________________________________________________________________

request_test.go

@@ -937,6 +937,36 @@ func TestGetWithCookies(t *testing.T) {
 	logResponse(t, resp)
 }
 
+func TestRequestScopes(t *testing.T) {
+	ts := createGetServer(t)
+	defer ts.Close()
+
+	c := dc()
+	c.SetQueryParam("client_param", "true").
+		SetQueryParams(map[string]string{"req_1": "jeeva", "req_3": "jeeva3"}).
+		SetDebug(true)
+	c.outputLogTo(ioutil.Discard)
+
+	queryParam := func(page, size int) func(r *Request) *Request {
+		return func(r *Request) *Request {
+			return r.SetQueryParam("page", strconv.FormatInt(int64(page), 10)).
+				SetQueryParam("size", strconv.FormatInt(int64(size), 10)).
+				SetQueryParam("request_no", strconv.FormatInt(time.Now().Unix(), 10))
+		}
+	}
+	resp, err := c.R().Scopes(queryParam(1, 100)).
+		SetHeader(hdrUserAgentKey, "Test Custom User agent").
+		Get(ts.URL + "/")
+
+	assertError(t, err)
+	assertEqual(t, http.StatusOK, resp.StatusCode())
+	assertEqual(t, "HTTP/1.1", resp.Proto())
+	assertEqual(t, "200 OK", resp.Status())
+	assertEqual(t, "TestGet: text response", resp.String())
+
+	logResponse(t, resp)
+}
+
 func TestPutPlainString(t *testing.T) {
 	ts := createGenServer(t)
 	defer ts.Close()