Is there some lib can facilitate the OPERATIONS of JSON in golang?

When I write python, I like to do that:

d = {"apple": "red", "book":["history", "art", "science"]}
print json.JSONEncoder().encode(d)

then I get the JSON string

'{"apple":"red","book":["history","art","science"]}'

but when I want to do that in Golang, things get more complicated, I have to define the struct first:

type Gadget struct {
    Apple string
    Book []string
}
g := Gadget{Apple: "red", Book: []string{"history", "art", "science"}}
bytes, _ := json.Marshal(g)
fmt.Println(string(bytes))

Is there some golang lib that can help me manipulate the JSON string like python?
I may have many JSON which have different struct to deal with. To define them all is a fussy work. I don't even think there's a lib cause there is no index operater overloading mechanism in golang.

What do you guys say?

^{Question would be off-topic as it asks for off-site resources, but it can be solved using the standard lib, so:}

You don't need a struct, you can just use embedded maps and slices which can model all data structures.

Your example:

err := json.NewEncoder(os.Stdout).Encode(map[string]interface{}{
	"apple": "red",
	"book": []interface{}{
		"history", "art", "science",
	},
})
fmt.Println(err)

Output (try it on the Go Playground):

{"apple":"red","book":["history","art","science"]}
<nil>