Extracting struct fields in Golang

15/08/2024 - GO

In this example we are going to extract struct field names and print the result. It can sometimes be useful to manage application configs or secrets further down the line.


package main

import (
	"fmt"
	"reflect"
)

func main() {
	var str Struct

	fields := str.Fields(Config{}, "/")
	for _, field := range fields {
		fmt.Println(field)
	}
}

type Struct struct {
	fields    []string
	separator string
}

func (s *Struct) Fields(source any, separator string) []string {
	s.separator = separator
	s.extract(reflect.ValueOf(source), "")

	return s.fields
}

func (s *Struct) extract(source reflect.Value, prefix string) {
	for i := 0; i < source.NumField(); i++ {
		field := source.Field(i)
		name := source.Type().Field(i).Name

		if field.Kind() == reflect.Struct {
			s.extract(field, prefix+name+s.separator)

			continue
		}

		s.fields = append(s.fields, prefix+name)
	}
}

type Config struct {
	ServiceName string
	Addresses   []string
	Logger      struct {
		Level string
	}
	HTTP struct {
		Server struct {
			Host    string
			Port    int
			Request struct {
				Timeout string
				Size    int
			}
		}
	}
	External
}

type External struct {
	ID    string
	Level struct {
		Severity string
	}
}

Test


ServiceName
Addresses
Logger/Level
HTTP/Server/Host
HTTP/Server/Port
HTTP/Server/Request/Timeout
HTTP/Server/Request/Size
External/ID
External/Level/Severity