How to append to a slice whose element type is not a named type in golang

php Xiaobian Banana will introduce you how to attach to a slice whose element type is not a named type in golang. In Golang, we can use the built-in append function to append elements to a slice, but if the element type of the slice is not a named type, that is, an anonymous type, we need to create a temporary slice first, then append the elements to the temporary slice, and finally Then copy the elements of the temporary slice back to the original slice. Doing this ensures that the original slice's data is not lost when appending elements. Next, we will detail the specific steps of this process.

Question content

I have two structures:

type responsequeryhotel struct {
    querystring *string `json:"querystring"`
    status   string `json:"status"`
    action   string `json:"action"`
    refcode  string `json:"refcode"`
    vendorid string `json:"vendorid"`
    searchtoken *string `json:"searchtoken"`
    data     struct {
        hotels []struct {
            data responsequeryhotelsdata `json:"data"`
        } `json:"hotels"`
    } `json:"data"`
}

type responsequeryhotelsdata struct {
    hotelidvendor      string `json:"hotelidvendor"`
    hotelname          string `json:"hotelname"`
    hoteladdress       string `json:"hoteladdress"`
    hoteldistrict      string `json:"hoteldistrict"`
    hotelcity          string `json:"hotelcity"`
    hotelprovince      string `json:"hotelprovince"`
    hotelcountry       string `json:"hotelcountry"`
    hotellat           string `json:"hotellat"`
    hotellng           string `json:"hotellng"`
    hotelprice         string `json:"hotelprice"`
    hoteldiscountprice string `json:"hoteldiscountprice"`
    hotelphotourl      string `json:"hotelphotourl"`
}

Now I need to append items to responsequeryhotel.data.hotels whose element type is not named name. So I tried this:

var output models.responsequeryhotel

var data models.responsequeryhotelsdata
output.data.hotels = append(output.data.hotels, data)

But I get this error:

cannot use data (variable of type models.ResponseQueryHotelsData) as struct{Data models.ResponseQueryHotelsData "json:\"data\""} value in argument to append

How should I attach items to output.data.hotels (there will be more than 1 responsequeryhotelsdata attached).

BTW, I can't change the structure (it's beyond my control).

Workaround

If you need to use it multiple times, define an alias for the same underlying type:

type hotel = struct {
    data responsequeryhotelsdata `json:"data"`
}
hotels := []hotel{
    {data: responsequeryhotelsdata{}},
    {data: responsequeryhotelsdata{}},
}

output.data.hotels = append(output.data.hotels, hotels...)

Or if you only need it once, declare the struct type in place:

hotels := []struct {
    Data ResponseQueryHotelsData `json:"data"`
}{
    {Data: ResponseQueryHotelsData{}},
    {Data: ResponseQueryHotelsData{}},
}

output.Data.Hotels = append(output.Data.Hotels, hotels...)

The

Assignability section of the golang specification states:

A value x of type v is assignable to a variable of type t ("x is assignable to t") if one of the following conditions is met:

• v is the same as t.
• v and t have the same underlying type, but not type parameters, and at least one of v or t is not a named type.
• v and t are channel types with the same element type, v is a bidirectional channel, and at least one of v or t is not a named type.
• t is an interface type but not a type parameter, and x implements t.
• x is the predeclared identifier nil and t is a pointer, function, slice, map, channel, or interface type, but not a type parameter.
• x is an untyped constant that can be represented by a value of type t.

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