How to pass field as parameter - go

Question

i want to pass field as parameter to return value from function
package main
import (
"fmt"
)
type s struct {
a int
b int
}
func c(s s) int {
var t int
t = s.a // how to change this to t=s.b just by pass parameter
return t
}
func main() {
fmt.Println(c(s{5, 8}))
}
some times i want to make t = s.a and other time i wanted t = s.b to return value 8 the question is how to pass it like parameter
https://play.golang.org/p/JisnrTxF2EY

Answer 1

You may add a 2nd parameter to signal which field you want, for example:
func c2(s s, field int) int {
var t int
switch field {
case 0:
t = s.a
case 1:
t = s.b
}
return t
}
Or a more convenient way is to pass the name of the field, and use reflection to get that field:
func c3(s s, fieldName string) int {
var t int
t = int(reflect.ValueOf(s).FieldByName(fieldName).Int())
return t
}
Or you may pass the address of the field, and assign the pointed value:
func c4(f *int) int {
var t int
t = *f
return t
}
Testing the above solutions:
x := s{5, 8}
fmt.Println("c2 with a:", c2(x, 0))
fmt.Println("c2 with b:", c2(x, 1))
fmt.Println("c3 with a:", c3(x, "a"))
fmt.Println("c3 with b:", c3(x, "b"))
fmt.Println("c4 with a:", c4(&x.a))
fmt.Println("c4 with b:", c4(&x.b))
Which will output (try it on the Go Playground):
c2 with a: 5
c2 with b: 8
c3 with a: 5
c3 with b: 8
c4 with a: 5
c4 with b: 8