How to Sort Go Struct Fields Alphabetically When Printing?

How to Render Struct Fields in Alphabetical Order

Structures in Go possess ordered fields. However, printing a struct using the formatting package (fmt) presents the fields in a non-alphabetical sequence. This article delves into techniques for sorting struct fields in alphabetical order.

Pre-define Fields in Alphabetical Order

The direct approach is to declare the struct with fields arranged in alphabetical order. This method is simple and ensures correct ordering regardless of reflection or custom formatting.

type T struct {
    A int
    B int
}

Implement the Stringer Interface

By implementing the Stringer interface with a String() method, you can customize how the struct is displayed. This method allows you to specify the order of fields in the output.

func (t T) String() string {
    return fmt.Sprintf("{%d %d}", t.A, t.B)
}

Employ Reflection

Reflection offers a comprehensive solution that applies to any struct regardless of type or package definition. It involves obtaining field names, sorting them, and then accessing field values based on the sorted names.

func printFields(st interface{}) string {
    t := reflect.TypeOf(st)

    names := make([]string, t.NumField())
    for i := range names {
        names[i] = t.Field(i).Name
    }
    sort.Strings(names)

    v := reflect.ValueOf(st)
    buf := &bytes.Buffer{}
    buf.WriteString("{")
    for i, name := range names {
        val := v.FieldByName(name)
        if !val.CanInterface() {
            continue
        }
        if i > 0 {
            buf.WriteString(" ")
        }
        fmt.Fprintf(buf, "%v", val.Interface())
    }
    buf.WriteString("}")

    return buf.String()
}

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