How to iterate through the fields of a struct in Go?

Question

Basically, the only way (that I know of) to iterate through the values of the fields of a struct is like this:
type Example struct {
    a_number uint32
    a_string string
}

//...

r := &Example{(2 << 31) - 1, "...."}:
for _, d:= range []interface{}{ r.a_number, r.a_string, } {
  //do something with the d
}

I was wondering, if there's a better and more versatile way of achieving []interface{}{ r.a_number, r.a_string, }, so I don't need to list each parameter individually, or alternatively, is there a better way to loop through a struct?

I tried to look through the reflect package, but I hit a wall, because I'm not sure what to do once I retrieve reflect.ValueOf(*r).Field(0).

Thanks!

Gopher · Accepted Answer

After you've retrieved the reflect.Value of the field by using Field(i) you can get a interface value from it by calling Interface(). Said interface value then represents the value of the field. There is no function to convert the value of the field to a concrete type as there are, as you may know, no generics in go. Thus, there is no function with the signature GetValue() T with T being the type of that field (which changes of course, depending on the field). The closest you can achieve in go is GetValue() interface{} and this is exactly what reflect.Value.Interface() offers. The following code illustrates how to get the values of each exported field in a struct using reflection: package main import ( "fmt" "reflect" ) func main() { x := struct{Foo string; Bar int }{"foo", 2} v := reflect.ValueOf(x) values := make([]interface{}, v.NumField()) for i := 0; i < v.NumField(); i++ { values[i] = v.Field(i).Interface() } fmt.Println(values) } https://play.golang.org/p/sCjhm0wC3_c Note: If the Fields in your struct are not exported then the v.Field(i).Interface() will give panic panic: reflect.Value.Interface: cannot return value obtained from unexported field or method.

Go Language

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