How Can I Easily Print Go Structs with Their Field Names and String() Methods?

Printing Structs with Field String()s

In this code:

type A struct {
    t time.Time
}

func main() {
    a := A{time.Now()}
    fmt.Println(a)
    fmt.Println(a.t)
}

notice that A doesn't implement the String() method, so fmt.Println(a) prints its native representation. Updating String() for every new field in a struct can be tedious.

Unfortunately, this behavior is inherent to the fmt package. However, a helper function using reflection can solve this issue:

func PrintStruct(s interface{}, names bool) string {
    v := reflect.ValueOf(s)
    t := v.Type()
    // To avoid panic if s is not a struct:
    if t.Kind() != reflect.Struct {
        return fmt.Sprint(s)
    }

    b := &bytes.Buffer{}
    b.WriteString("{")
    for i := 0; i < v.NumField(); i++ {
        if i > 0 {
            b.WriteString(" ")
        }
        v2 := v.Field(i)
        if names {
            b.WriteString(t.Field(i).Name)
            b.WriteString(":")
        }
        if v2.CanInterface() {
            if st, ok := v2.Interface().(fmt.Stringer); ok {
                b.WriteString(st.String())
                continue
            }
        }
        fmt.Fprint(b, v2)
    }
    b.WriteString("}")
    return b.String()
}

This function uses reflection to iterate over struct fields and call their String() methods if available.

Usage:

fmt.Println(PrintStruct(a, true))

Optionally, add a String() method to the struct that calls PrintStruct():

func (a A) String() string {
    return PrintStruct(a, true)
}

Now, struct fields with String() will be printed automatically.

Notes:

• Export any private fields to make them accessible to reflection.
• Add field names for better readability (but it's optional).
• This approach works even if the value is not a struct, making it versatile.

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