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     amp Example  2  lt  lt  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

User · Answer

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.

User · 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  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  lt  v NumField    i             values i    v Field i  Interface              fmt Println values

User · Answer

Taking Chetan Kumar solution and in case you need to apply to a map string int  package main  import        fmt       reflect     type BaseStats struct       Hp           int     HpMax        int     Mp           int     MpMax        int     Strength     int     Speed        int     Intelligence int    type Stats struct       Base map string int     Modifiers   string    func StatsCreate stats BaseStats  Stats       s    Stats          Base  make map string int                Iterate through the fields of a struct     v    reflect ValueOf stats      typeOfS    v Type        for i    0  i lt  v NumField    i             val    v Field i  Interface    int          s Base typeOfS Field i  Name    val           return s    func  s Stats  GetBaseStat id string  int       return s Base id      func main         m    StatsCreate BaseStats 300  300  300  300  10  10  10        fmt Println m GetBaseStat  Hp

User · Answer

Maybe too late      but there is another solution that you can find the key and value of structs and iterate over that package main  import        quot fmt quot       quot reflect quot     type person struct       firsName string     lastName string     iceCream   string    func main         u    struct           myMap    map int int         mySlice    string         myPerson person                myMap    map int int 1  10  2  20           mySlice    string  quot red quot    quot green quot            myPerson  person              firsName   quot Esmaeil quot               lastName   quot Abedi quot               iceCream    string  quot Vanilla quot    quot chocolate quot                         v    reflect ValueOf u      for i    0  i  lt  v NumField    i             fmt Println v Type   Field i  Name          fmt Println  quot  t quot   v Field i            and there is no  panic  for v Field i

[go] Iterate through the fields of a struct in Go

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