using reflection in Go to get the name of a struct - go

Question

I found this question with this great answers:
How to find a type of a object in Golang?
I played around with the answer and tried to get the name of a struct in the same way:
package main
import (
"fmt"
"reflect"
)
type Ab struct {
}
func getType(myvar interface{}) string {
return reflect.TypeOf(myvar).Name()
}
func main() {
fmt.Println("Hello, playground")
tst := "string"
tst2 := 10
tst3 := 1.2
tst4 := new(Ab)
fmt.Println(getType(tst))
fmt.Println(getType(tst2))
fmt.Println(getType(tst3))
fmt.Println(getType(tst4))
}
Go playground: http://play.golang.org/p/tD8mygvETH
But the output is:
Hello, playground
string
int
float64
Program exited.
Expected output would be:
Hello, playground
string
int
float64
Ab
Program exited.
I tried to figure out by reading the documentation but didn't find the issue about that. So, sorry for the very general question, but:
What's the reason, reflect.TypeOf().Name() does not work with (this) struct(s)?

Answer 1

In your example you pass a value of pointer type (*Ab), not a struct type.
Sticking to Type.Name()
If it is not a pointer, Type.Name() will properly return Ab. In case of pointer if you still want the struct's name, you can use Type.Elem() to get the element's type:
func getType(myvar interface{}) string {
if t := reflect.TypeOf(myvar); t.Kind() == reflect.Ptr {
return "*" + t.Elem().Name()
} else {
return t.Name()
}
}
Testing it:
tst4 := Ab{}
tst5 := new(Ab)
fmt.Println(getType(tst4))
fmt.Println(getType(tst5))
Output (try your modified example on the Go Playground):
Ab
*Ab
Note:
Note that as Type.Name() does not resolve pointers, it would not work if the value passed is a pointer to pointer, e.g. **Ab, while as Type.String() automatically resolves pointers, would work in this case too.
We can easily make our getType() function to work with **Ab too (or with any depth of pointers):
func getType(myvar interface{}) (res string) {
t := reflect.TypeOf(myvar)
for t.Kind() == reflect.Ptr {
t = t.Elem()
res += "*"
}
return res + t.Name()
}
Calling it with values:
tst4 := Ab{}
tst5 := new(Ab)
tst6 := &tst5 // type of **Ab
tst7 := &tst6 // type of ***Ab
Output (try it on the Go Playground):
Ab
*Ab
**Ab
***Ab
Using Type.String()
A simpler and better approach would be to use Type.String() instead of Type.Name() which automatically handles pointers and also includes package name. E.g.:
func getType(myvar interface{}) string {
return reflect.TypeOf(myvar).String()
}
For the modified example it outputs:
string
int
float64
main.Ab
*main.Ab
Try this variant on the Go Playground.

Answer 2

fmt has a cool %T tag as well
package main
import (
"fmt"
"net/http"
)
type Potato struct {
}
func main() {
fmt.Printf("I have a %T, an %T and a %T\n", Potato{}, http.StatusMultipleChoices, &http.Response{})
}
outputs I have a main.Potato, an int and a *http.Response
https://play.golang.org/p/6z7_0BSitm

Answer 3

The problem is new returns pointer, following should get the desired result.
package main
import (
"fmt"
"reflect"
)
type Ab struct {
}
func getType(myvar interface{}) {
valueOf := reflect.ValueOf(myvar)
if valueOf.Type().Kind() == reflect.Ptr {
fmt.Println(reflect.Indirect(valueOf).Type().Name())
} else {
fmt.Println(valueOf.Type().Name())
}
}
func main() {
fmt.Println("Hello, playground")
tst := "string"
tst2 := 10
tst3 := 1.2
tst4 := new(Ab)
getType(tst)
getType(tst2)
getType(tst3)
getType(tst4)
}
Output is
Hello, playground
string
int
float64
Ab