Print the Type of variable from struct

Getting Help
1

I am trying to store the type of variable in a struct and print the value of it.
code:-

package main

import (
	"fmt"
	"reflect"
)

type a struct {
	typ reflect.Type
	s   string
}

func main() {
	ad := &a{
		s: "akhil",
	}
	ad.typ = ak()
	fmt.Println(ad)
}

func ak() reflect.Type {
	return reflect.TypeOf(int32(0))
}

OUTPUT:
&{0x49b360 akihl}

In place of address or something how to print the type.

Thanks.

2

You can print that field fmt.Println(ad.typ). But if you want print struct and show type that hold in value of typ field you need to implement String method for a struct type.

func (v a) String() string {
	return fmt.Sprintf("{%v %v}", v.typ, v.s)
}
3

For ex if my struct has 10 values than the i have print all ten values ?

That is difficult.

4 
type ColumnType struct {
	name string

	hasNullable       bool
	hasLength         bool
	hasPrecisionScale bool

	nullable     bool
	length       int64
	databaseType string
	precision    int64
	scale        int64
	scanType     reflect.Type
}

This is a struct in sql package. I have stored the type in scanType field. so when i am printing it it print the address.

{name:A hasNullable:true hasLength:true hasPrecisionScale:true nullable:true length:12 databaseType:DECIMAL precision:10
scale:2 scanType:0x4c5100}


{name:B hasNullable:true hasLength:true hasPrecisionScale:true nullable:true length:7 databaseType:DECIMAL precision:5 scale:2 scanType:0x4c5100}

If i use (variable.scanType) in print it will show us that no that type of field or method because it is not exported.

How to solve this is?

Thanks

5

I think you can use this package https://github.com/davecgh/go-spew/ alternative to fmt.Println for debugging deep nested struct. I’v tried and it can inspect the value of type reflect.Type.

6

From go itself we cant print it ?.

7

Yes I think no function from standard package can do like that.

8

Ok…Thanks.

9

I am not quite sure what you want to do. But you can use the Stringer interface to define how your types should be represented.

package main

import (
	"fmt"
)

type Outer struct {
	A InnerA
	B InnerB
}

func (o Outer) String() string {
	return fmt.Sprintf("Outer(%s, %s)", o.A, o.B)
}

type InnerA struct {
	S string
}

func (a InnerA) String() string {
	return fmt.Sprintf("A(S=\"%s\")", a.S)
}

type InnerB struct {
	S string
}

func (b InnerB) String() string {
	return fmt.Sprintf("B(S=\"%s\")", b.S)
}

func main() {
	o := Outer{A: InnerA{S: "in A"}, B: InnerB{S: "in B"}}
	fmt.Printf("using Stringer: %s\n", o)
}

Output:

using Stringer: Outer(A(S="in A"), B(S="in B"))

https://play.golang.com/p/fJlafDbbyFw

10

@lutzhorn Sorry, I didn’t get you. can u explain me with an example with printing the types of a variable.

Thanks.

11

Use %T to print the type of a value.

package main

import (
	"fmt"
)

type Outer struct {
	A InnerA
	B InnerB
}

func (o Outer) String() string {
	return fmt.Sprintf("%T(%s, %s)", o, o.A, o.B)
}

type InnerA struct {
	S string
}

func (a InnerA) String() string {
	return fmt.Sprintf("%T(%T(\"%s\"))", a, a.S, a.S)
}

type InnerB struct {
	S string
}

func (b InnerB) String() string {
	return fmt.Sprintf("%T(%T(\"%s\"))", b, b.S, b.S)
}

func main() {
	o := Outer{A: InnerA{S: "in A"}, B: InnerB{S: "in B"}}
	fmt.Printf("using Stringer: %s\n", o)
}

Output:

using Stringer: main.Outer(main.InnerA(string("in A")), main.InnerB(string("in B")))

https://play.golang.com/p/nwpyc5aE3s3

12

Thanks @lutzhorn

13

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