How to Print Go Struct Fields in Alphabetical Order?

How to Print Struct Fields in Alphabetical Order

In Go, a struct's fields are ordered as they are defined. Therefore, if you want to obtain an output of a struct sorted by the fields' names, the simplest solution is to arrange the fields alphabetically in the struct type declaration.

For example:

type T struct {
    A int
    B int
}

However, if you cannot modify the field order due to memory layout considerations, you have other options:

1. Implement the Stringer Interface

By implementing the String() method, you can control the output of your struct:

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

2. Use Reflection

Reflection provides a flexible way to iterate over struct fields and obtain their values:

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()
}

By invoking the printFields() function, you can obtain the sorted output of your struct.

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