Golang Viper config read into struct

config.go

package main

import (
	"fmt"

	"github.com/spf13/viper"
)

// Create private data struct to hold config options.
type config struct {
	Hostname string `yaml:"hostname"`
	Port     string `yaml:"port"`
}

// Create a new config instance.
var (
  conf *config
)
 
// Read the config file from the current directory and marshal
// into the conf config struct.
func getConf() *config {
	viper.AddConfigPath(".")
	viper.SetConfigName("config")
	err := viper.ReadInConfig()

	if err != nil {
		fmt.Printf("%v", err)
	}

	conf := &config{}
	err = viper.Unmarshal(conf)
	if err != nil {
		fmt.Printf("unable to decode into config struct, %v", err)
	}

	return conf
}

// Initialization routine.
func init() {
  // Retrieve config options.
  conf = getConf()
}

// Main program.
func main() {
  // Print the config options from the new conf struct instance.
  fmt.Printf("Hostname: %v\n", conf.Hostname) 
  fmt.Printf("Port: %v\n", conf.Port) 
}

config.yml

hostname: "localhost"
port: "9001"

I have replaced yaml tag to mapstructure and code become workable

Why on line 31 you used a pointer to the config struct?
What's the reasoning behind it?

@maxiride because Unmarshal mutates the members of the Config struct, which can only be done if you pass a reference to the object.

Just to clarify one point (I wasted some time because of it).
In the example, I don't think the yaml field tags have any effect.
My understanding is that they only come into play if yaml is being loaded directly into a struct; in this case, the yaml is first loaded into a viper map (by the ReadInConfig() call), and subsequently unmarshalled into the struct (by the Unmarshal() call).

Can confirm. I can load them w/o any issue on .toml file w/o struct tags.

Kind of interesting, you don't actually need double quotes within your config struct. This would also work:

// Create private data struct to hold config options.
type config struct {
	Hostname string `yaml:hostname`
	Port     string `yaml:port`
}

Hmm. It didn't work. Maybe because I'd used snake_case

upd
Yeah, I was right: spf13/viper#125

How to make this work for TOML file?

what if i have nested config in yaml file. i did not work
thirdparty:
api:
key: "key1"
"baseUrl": "example.com"