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

Question

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 :)

Answer 1

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"))
}

Answer 2

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)
}