How to find the type of an object in Go?

Question

How do I find the type of an object in Go? In Python, I just use typeof to fetch the type of object. Similarly in Go, is there a way to implement the same ?

Answer 1

To be short, please use fmt.Printf("%T", var1) or its other variants in the fmt package.

Answer 2

The Go reflection package has methods for inspecting the type of variables.

The following snippet will print out the reflection type of a string, integer and float.

package main

import (
    "fmt"
    "reflect"
)

func main() {

    tst := "string"
    tst2 := 10
    tst3 := 1.2

    fmt.Println(reflect.TypeOf(tst))
    fmt.Println(reflect.TypeOf(tst2))
    fmt.Println(reflect.TypeOf(tst3))

}

Output:

Hello, playground
string
int
float64

see: http://play.golang.org/p/XQMcUVsOja to view it in action.

More documentation here: http://golang.org/pkg/reflect/#Type

Answer 3

You can check the type of any variable/instance at runtime either using the "reflect" packages TypeOf function or by using fmt.Printf():

package main

import (
   "fmt"
   "reflect"
)

func main() {
    value1 := "Have a Good Day"
    value2 := 50
    value3 := 50.78

    fmt.Println(reflect.TypeOf(value1 ))
    fmt.Println(reflect.TypeOf(value2))
    fmt.Println(reflect.TypeOf(value3))
    fmt.Printf("%T",value1)
    fmt.Printf("%T",value2)
    fmt.Printf("%T",value3)
}

Answer 4

Use the reflect package:

Package reflect implements run-time reflection, allowing a program to manipulate objects with arbitrary types. The typical use is to take a value with static type interface{} and extract its dynamic type information by calling TypeOf, which returns a Type.

package main

import (
    "fmt"
    "reflect"
)

func main() {
    b := true
    s := ""
    n := 1
    f := 1.0
    a := []string{"foo", "bar", "baz"}

    fmt.Println(reflect.TypeOf(b))
    fmt.Println(reflect.TypeOf(s))
    fmt.Println(reflect.TypeOf(n))
    fmt.Println(reflect.TypeOf(f))
    fmt.Println(reflect.TypeOf(a))
}

Produces:

bool
string
int
float64
[]string

Playground

Example using ValueOf(i interface{}).Kind():

package main

import (
    "fmt"
    "reflect"
)

func main() {
    b := true
    s := ""
    n := 1
    f := 1.0
    a := []string{"foo", "bar", "baz"}

    fmt.Println(reflect.ValueOf(b).Kind())
    fmt.Println(reflect.ValueOf(s).Kind())
    fmt.Println(reflect.ValueOf(n).Kind())
    fmt.Println(reflect.ValueOf(f).Kind())
    fmt.Println(reflect.ValueOf(a).Index(0).Kind()) // For slices and strings
}

Produces:

bool
string
int
float64
string

Playground

Answer 5

If we have this variables:

var counter int = 5
var message string  = "Hello"
var factor float32 = 4.2
var enabled bool = false

1: fmt.Printf %T format : to use this feature you should import "fmt"

fmt.Printf("%T \n",factor )   // factor type: float32

2: reflect.TypeOf function : to use this feature you should import "reflect"

fmt.Println(reflect.TypeOf(enabled)) // enabled type:  bool

3: reflect.ValueOf(X).Kind() : to use this feature you should import "reflect"

fmt.Println(reflect.ValueOf(counter).Kind()) // counter type:  int

Answer 6

I would stay away from the reflect. package. Instead use %T

package main

import (
    "fmt"
)

func main() {
    b := true
    s := ""
    n := 1
    f := 1.0
    a := []string{"foo", "bar", "baz"}

    fmt.Printf("%T\n", b)
    fmt.Printf("%T\n", s)
    fmt.Printf("%T\n", n)
    fmt.Printf("%T\n", f)
    fmt.Printf("%T\n", a)
 }