Go - empty slice when return by gin.Context.JSON

if resp is struct with slice member like following:

type MyStruct struct {
    Data  []struct {
        Name        string `json:"name"`
    } `json:"data"`
}

func Something(c *gin.Context) {
	result := make(chan MyStruct, 1)
	go func() {
		resp, _ := Calculate()  // if return empty slice
        fmt.Println(result)     // output: {[]}
		result <- resp
	}()
	
	c.JSON(http.StatusOK, <-result) // output: {"data": null}
}

Is it possible make the last output <-result to {"data": []}?

The fmt package prints nil slices the same as empty slices: [].

The json/encoding package makes a distinction between nil slices and empty slices. A nil slice is encode as nil and an empty slice is encoded as [].

To get the expected output, set the Data field to an empty slice:

resp.Data = []struct {
	Name string `json:"name"`
}{}

To make this easier, declare a named type for the Data field:

type Data struct {
	Name string `json:"name"`
}
type MyStruct struct {
	Data []Data `json:"data"`
}

Set the field to the empty slice using:

resp.Data = []Data{}

Combine this assignment with the variable declaration by using a short variable declaration and a composite literal containing the empty slice:

resp := MyStruct{Data: []Data{}}