How to get empty list [] instead of null for json.Marshal of []byte?

user_1061008 0
Viewed 35

It easy to get an empty list when working with string by using []string{}:

import (
    "encoding/json"
    "fmt"
)

func main() {
    slice1 := []string{} // non-nil but zero-length
    json1, _ := json.Marshal(slice1)
    fmt.Printf("%s\n", json1) // []
}

The output of code above is [], BUT when I work with []byte even using []byte{} returns "". How should I get an empty list like what I get in []string{}?

import (
    "encoding/json"
    "fmt"
)

func main() {
    slice2 := []byte{}
    json2, _ := json.Marshal(slice2)
    fmt.Printf("%s\n", json2) // ""
}
go slice
1 Answers

See the docs:

Array and slice values encode as JSON arrays, except that []byte encodes as a base64-encoded string, and a nil slice encodes as the null JSON value.

The part in bold is why you get "". If you want [] from []byte{}, you need a custom named []byte type that implements the json.Marshaler interface.

Or, if you're looking for a "slice of integers", then use []N where N can be any of the basic integer types just not the uint8 type. The uint8 type will not work because byte is an alias of uint8 so []uint8 is identical to []byte and json.Marshal will output "" for that as well.

user_9659000
Related