How to find a type of an object in Go?

问题

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 ?

Here is the container from which I am iterating:

for e := dlist.Front(); e != nil; e = e.Next() {
    lines := e.Value
    fmt.Printf(reflect.TypeOf(lines))
}

I am not able to get the type of the object lines in this case which is an array of strings.

回答1:

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))

}

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

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

回答2:

I found 3 ways to return a variable's type at runtime:

Using string formatting

func typeof(v interface{}) string {
    return fmt.Sprintf("%T", v)
}

Using reflect package

func typeof(v interface{}) string {
    return reflect.TypeOf(v).String()
}

Using type assertions

func typeof(v interface{}) string {
    switch v.(type) {
    case int:
        return "int"
    case float64:
        return "float64"
    //... etc
    default:
        return "unknown"
    }
}

Every method has a different best use case:

string formatting - short and low footprint (not necessary to import reflect package)
reflect package - when need more details about the type we have access to the full reflection capabilities
type assertions - allows grouping types, for example recognize all int32, int64, uint32, uint64 types as "int"

回答3:

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

回答4:

To get a string representation:

From http://golang.org/pkg/fmt/

%T a Go-syntax representation of the type of the value

package main
import "fmt"
func main(){
    types := []interface{} {"a",6,6.0,true}
    for _,v := range types{
        fmt.Printf("%T\n",v)
    }
}

Outputs:

string
int
float64
bool

回答5:

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)
 }

回答6:

Best way is using reflection concept in Google.
reflect.TypeOf gives type along with the package name
reflect.TypeOf().Kind() gives underlining type

回答7:

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

回答8:

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)
}

回答9:

To get the type of fields in struct

package main

import (
  "fmt"
  "reflect"
)

type testObject struct {
  Name   string
  Age    int
  Height float64
}

func main() {
   tstObj := testObject{Name: "yog prakash", Age: 24, Height: 5.6}
   val := reflect.ValueOf(&tstObj).Elem()
   typeOfTstObj := val.Type()
   for i := 0; i < val.NumField(); i++ {
       fieldType := val.Field(i)
       fmt.Printf("object field %d key=%s value=%v type=%s \n",
          i, typeOfTstObj.Field(i).Name, fieldType.Interface(),
          fieldType.Type())
   }
}

Output

object field 0 key=Name value=yog prakash type=string 
object field 1 key=Age value=24 type=int 
object field 2 key=Height value=5.6 type=float64

See in IDE https://play.golang.org/p/bwIpYnBQiE

回答10:

you can use reflect.TypeOf.

basic type(e.g.: int, string): it will return its name (e.g.: int, string)
struct: it will return something in the format <package name>.<struct name> (e.g.: main.test)

回答11:

reflect package comes to rescue:

reflect.TypeOf(obj).String()

Check this demo

回答12:

You can just use the fmt package fmt.Printf() method, more information: https://golang.org/pkg/fmt/

example: https://play.golang.org/p/aJG5MOxjBJD

来源：https://stackoverflow.com/questions/20170275/how-to-find-a-type-of-an-object-in-go

标签

go-reflect