Convert from string to int (and throw error if unsuccessful)

My apologies if this is a beginner question, but I simply can't seem to find any solution for this. I'm trying to take an argument that can be either a string or an int, depending on the context, and I need to determine which type, (then convert it to int if it is indeed that type.)

Thank you

For example,

package main

import (
	"errors"
	"fmt"
	"strconv"
)

func IntConv(arg interface{}) (int, error) {
	switch x := arg.(type) {
	case int:
		return x, nil
	case string:
		return strconv.Atoi(x)
	}
	return 0, errors.New("IntConv: invalid argument ")
}

func main() {
	fmt.Println(IntConv(7))
	fmt.Println(IntConv("42"))
}

http://golang.org/pkg/strconv/#Atoi

func Atoi

func Atoi(s string) (i int, err error)
Atoi is shorthand for ParseInt(s, 10, 0).

This is an update. To clarify, since Atoi accepts string, then trying to pass an int will cause a compile time error. If you need a check during runtime, then you can do something like this.

package main

import (
    "fmt"
    "strconv"
    "errors"
)

func toInt(data interface{}) (n int, err error) {
    switch t := data.(type) {
    case int:
	    return t, nil
    case string:
	    return strconv.Atoi(t)
    default:
	    return 0, errors.New(fmt.Sprintf("Invalid type received: %T", t))
    }

    panic("unreachable!")
}

func main() {
    var (
	    n int
	    err error
    )

    n, _ = toInt("1")
    fmt.Println(n)

    n, _ = toInt(2)
    fmt.Println(n)

    n, err = toInt(32.3)
    fmt.Println(err)
}

I'm a bit late to the party, but you could also use fmt.Sprintf:

import "fmt"

func ConvertToString(x interface{}) string {
	return fmt.Sprintf("%v", x)
}

Passing "%v" to Sprintf tells it to format it using the best format it knows, which essentially just means "convert x to a string". This is shorter (and perhaps easier to understand) than the other solutions, but has the disadvantage that it'll allow inputs that aren't ints or strings.