Golang remap interface go-cache - go

Question

I've got a struct like below:
type Page struct {
title string
url string
}
and a map of structs:
var mostViewed = make(map[int]Page)
With go-cache, I store the map with a TTL time.
c.Set("data", mostViewed, 60*time.Minute)
But, once I recover "data" key, how could I assing it back to a map?
a, _ := c.Get("data")
fmt.Printf("%+v\n", a)
out: map[17:{title:xxx, url:yyy}]
I tried something like:
z := map[int]Page{a}
Any clue? It's like "remapping" a mapped string.

Answer 1

You get an interface{} type back, but you know what it is, so you need to use a type assertion to cast it back to a map[int]Page. Here is a quick external resource. https://newfivefour.com/golang-interface-type-assertions-switch.html
Here is an example
https://play.golang.org/p/lGseg88K1m
type Page struct {
title string
url string
}
func main() {
m := make(map[int]Page)
m[1] = Page{"hi", "there"}
iface := makeIface(m)
// use type assertion to cast it back to a map
if mapAgain, ok := iface.(map[int]Page); ok {
// it really is a map[int]Page
fmt.Printf("%+v\n", mapAgain)
} else {
// its not actually a map[int]Page
fmt.Println("oops")
}
// alternatively use a type-switch if it could be multiple types
switch v := iface.(type) {
case map[int]Page:
//yay
fmt.Printf("%+v\n", v)
case string:
// its a string
fmt.Println(v)
default:
// something we didn't account for
}
}
func makeIface(m map[int]Page) interface{} {
return m
}
Edit: as a side note, you probably want to make your map type map[int]*Page because if you did something like this:
page := m[1]
page.url = "different"
fmt.Println(page) // prints url="different"
fmt.Println(m[1].url) // remains unchanged
Because page would be a copy of what is in the map, not the Page in the map itself.