How to pretty print variables

If your goal is to avoid importing a third-party package, your other option is to use json.MarshalIndent:

x := map[string]interface{}{"a": 1, "b": 2}
b, err := json.MarshalIndent(x, "", "  ")
if err != nil {
    fmt.Println("error:", err)
}
fmt.Print(string(b))

Output:

{
    "a": 1,
    "b": 2
}

Working sample: http://play.golang.org/p/SNdn7DsBjy

Nevermind, I found one: https://github.com/davecgh/go-spew

// import "github.com/davecgh/go-spew/spew"
x := map[string]interface{}{"a":1,"b":2}
spew.Dump(x)

Would give an output:

(map[string]interface {}) (len=2) {
 (string) (len=1) "a": (int) 1,
 (string) (len=1) "b": (int) 2
}

I came up to use snippet like this:

func printMap(m map[string]string) {
    var maxLenKey int
    for k, _ := range m {
        if len(k) > maxLenKey {
            maxLenKey = len(k)
        }
    }

    for k, v := range m {
        fmt.Println(k + ": " + strings.Repeat(" ", maxLenKey - len(k)) + v)
    }
}

The output will be like this:

short_key:       value1
really_long_key: value2

Tell me, if there's some simpler way to do the same alignment.

If you want pretty coloured output, you can use pp.

https://github.com/k0kubun/pp

import "github.com/k0kubun/pp"
...
pp.Print(m)