Iterate through the fields of a struct in Go
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 (play):
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)
}
Go 1.17 (Q3 2021) should add a new option, through commit 009bfea and CL 281233, fixing issue 42782.
reflect: add VisibleFields function
When writing code that reflects over a struct type, it's a common requirement to know the full set of struct fields, including fields available due to embedding of anonymous members while excluding fields that are erased because they're at the same level as another field with the same name.
The logic to do this is not that complex, but it's a little subtle and easy to get wrong.
This CL adds a new
reflect.VisibleFields()
function to thereflect
package that returns the full set of effective fields that apply in a given struct type.
fields := reflect.VisibleFields(typ)
for j, field := range fields {
...
}
Example,
type employeeDetails struct {
id int16
name string
designation string
}
func structIterator() {
fields := reflect.VisibleFields(reflect.TypeOf(struct{ employeeDetails }{}))
for _, field := range fields {
fmt.Printf("Key: %s\tType: %s\n", field.Name, field.Type)
}
}
If you want to Iterate through the Fields and Values of a struct then you can use the below Go code as a reference.
package main
import (
"fmt"
"reflect"
)
type Student struct {
Fname string
Lname string
City string
Mobile int64
}
func main() {
s := Student{"Chetan", "Kumar", "Bangalore", 7777777777}
v := reflect.ValueOf(s)
typeOfS := v.Type()
for i := 0; i< v.NumField(); i++ {
fmt.Printf("Field: %s\tValue: %v\n", typeOfS.Field(i).Name, v.Field(i).Interface())
}
}
Run in playground
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.