How do I write a function for multiple types in Golang?

Question

I'm trying to write a helper function that can take in different custom Types in Golang, but I can't figure out how to do it exactly the way I want. Here's the situation (incidentally, I'm building an API that returns JSON objects implementing HAL protocol. This just means that resources and relationships are returned as links and not simply ID').

I have a number of models in my app, such as Student, Principal, School, etc... Each of these models has many fields, some same, some different. Ideally, I'd like a function that can iterate through the fields of a struct, and change another field in the struct. The big challenge is that these structs can be of type Student, Principal, School, etc...

Models:

type Person struct {
    halgo.Links
    Id        bson.ObjectId 
    Firstname string        
    Lastname  string        
    Email     string        
}

type Student struct {
    Person `bson:",inline"`

    School mgo.DBRef
}

type School struct {
    Id      bson.ObjectId
    Address []string     
    Name    string       
    Description string
}

Then, I'd like a function that can basically take any of these structs, iterate through the fields (using reflect), and do something with each field.

I've tried a function that takes interface{} but the problem is you have to type-assert the argument to have access to any of the fields. And even once you have that, you'll still have to write individual functions for each type/model anyways.:

func GenerateLinksHelper(m interface{}) {
...
}

Ultimately, I'm trying to find a way to write a function that takes in a somewhat arbitrary struct and perform operations on fields that may or may not be there.

Answer 1

I am not sure to understand what you are trying to do, but with reflection, you can see if a field exists or not and then do something with it.

Example derived from the 'laws of reflection' article (http://blog.golang.org/laws-of-reflection). Play: http://play.golang.org/p/neU3j2MYvz

package main

import (
    "fmt"
    "reflect"
)

type T1 struct {
    A int
    B string
}

type T2 struct {
    A int
}

func fct(i interface{}) {
    s := reflect.ValueOf(i).Elem()
    typeOfT := s.Type()
    for i := 0; i < s.NumField(); i++ {
        f := s.Field(i)
        if typeOfT.Field(i).Name == "B" {
            fmt.Printf("I am %s and I have a field B: %s\n", typeOfT.Name(), f.Interface())
        }
    }

}

func main() {
    t1 := T1{23, "skidoo"}
    t2 := T2{23}
    fct(&t1)
    fct(&t2)
}