How to convert interface to int64 in Go


Type Assertion

To convert interface to int64 in Go, Using Type Assertion.

A type assertion provides access to an interface value's underlying concrete value.

package main

import "fmt"

// t := i.(T)
// t, ok := i.(T)

func main() {

  var v interface{} = 1

  // interface to int
  i, ok := v.(int)
  fmt.Println(i, ok)

  // int to int64
  i64 := int64(i)
  s := fmt.Sprintf("Type: %T, %d", i64, i64)

  i64 = v.(int64) // panic
1 true

Type: int64, 1

panic: interface conversion: interface {} is int, not int64

If i does not hold a T, the statement will trigger a panic.

Type switches

A type switch is like a regular switch statement, but the cases in a type switch specify types (not values), and those values are compared against the type of the value held by the given interface value.

func i2num(i interface{}) (int64, error) {

  switch v := i.(type) {
  case int64:
    return v, nil
  case int:
    return int64(v), nil
  case string:
    return strconv.ParseInt(v, 10, 64)
    return 0, errors.New("type error")

// i, err := i2num("34")

// i, err := i2num("34.2")
// fmt.Println(i, err)
0 strconv.ParseInt: parsing "34.2": invalid syntax

Related Tags