(Go) How to use toml files?

A small update for the year 2019 - there is now newer alternative to BurntSushi/toml with a bit richer API to work with .toml files:

pelletier/go-toml (and documentation)

For example having config.toml file (or in memory):

[postgres]
user = "pelletier"
password = "mypassword"

apart from regular marshal and unmarshal of the entire thing into predefined structure (which you can see in the accepted answer) with pelletier/go-toml you can also query individual values like this:

config, err := toml.LoadFile("config.toml")

if err != nil {
    fmt.Println("Error ", err.Error())
} else {

    // retrieve data directly

    directUser := config.Get("postgres.user").(string)
    directPassword := config.Get("postgres.password").(string)
    fmt.Println("User is", directUser, " and password is", directPassword)

    // or using an intermediate object

    configTree := config.Get("postgres").(*toml.Tree)
    user := configTree.Get("user").(string)
    password := configTree.Get("password").(string)
    fmt.Println("User is", user, " and password is", password)

    // show where elements are in the file

    fmt.Printf("User position: %v\n", configTree.GetPosition("user"))
    fmt.Printf("Password position: %v\n", configTree.GetPosition("password"))

    // use a query to gather elements without walking the tree

    q, _ := query.Compile("$..[user,password]")
    results := q.Execute(config)
    for ii, item := range results.Values() {
        fmt.Println("Query result %d: %v", ii, item)
    }
}

UPDATE

There is also spf13/viper that works with .toml config files (among other supported formats), but it might be a bit overkill in many cases.

UPDATE 2

Viper is not really an alternative (credits to @GoForth).

First get BurntSushi's toml parser:

go get github.com/BurntSushi/toml

BurntSushi parses toml and maps it to structs, which is what you want.

Then execute the following example and learn from it:

package main

import (
    "github.com/BurntSushi/toml"
    "log"
)

var tomlData = `title = "config"
[feature1]
enable = true
userids = [
  "12345", "67890"
]

[feature2]
enable = false`

type feature1 struct {
    Enable  bool
    Userids []string
}

type feature2 struct {
    Enable bool
}

type tomlConfig struct {
    Title string
    F1    feature1 `toml:"feature1"`
    F2    feature2 `toml:"feature2"`
}

func main() {
    var conf tomlConfig
    if _, err := toml.Decode(tomlData, &conf); err != nil {
        log.Fatal(err)
    }
    log.Printf("title: %s", conf.Title)
    log.Printf("Feature 1: %#v", conf.F1)
    log.Printf("Feature 2: %#v", conf.F2)
}

Notice the tomlData and how it maps to the tomlConfig struct.

See more examples at https://github.com/BurntSushi/toml