Difference between &Struct{} vs Struct{}

Question

Is there a reason why I should create a struct using &StructName{} instead of Struct{}? I see many examples using the former syntax, even in the Effective Go Page but I really can not understand why.

Additional Notes: I'm not sure whether I explained my problem well with these two approaches so let me refine my question.

I know that by using the & I will recieve a pointer instead of a value however I would like to know why would I use the &StructName{} instead of the StructName{}. For example, is there any benefits of using:

func NewJob(command string, logger *log.Logger) *Job {
    return &Job{command, logger}
}

instead of:

func NewJob(command string, logger *log.Logger) Job {
    return Job{command, logger}
}

Maleck13 · Accepted Answer · 2015-11-08 16:53:18Z

20

Well, they will have different behavior. Essentially if you want to modify state using a method on a struct, then you will need a pointer, otherwise a value will be fine. Maybe an example will be better:

package main
import "fmt"



type test_struct struct {
  Message string
}

func (t test_struct)Say (){
   fmt.Println(t.Message)
}

func (t test_struct)Update(m string){
  t.Message = m; 
}

func (t * test_struct) SayP(){
   fmt.Println(t.Message)
}

func (t* test_struct) UpdateP(m string)  {
  t.Message = m;
}

func main(){
  ts := test_struct{}
  ts.Message = "test";
  ts.Say()
  ts.Update("test2")
  ts.Say() // will still output test

  tsp := &test_struct{}
  tsp.Message = "test"
  tsp.SayP();
  tsp.UpdateP("test2")
  tsp.SayP() // will output test2

}

And you can run it here go playground

edited Nov 8, 2015 at 16:53

answered Nov 8, 2015 at 16:43

Maleck13

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Comments

John · Accepted Answer · 2015-11-08 14:33:48Z

7

Assuming you know the general difference between a pointer and a value:

The first way allocates a struct and assigns a pointer to that allocated struct to the variable p1.

p1 := &StructName{}

The second way allocates a struct and assigns a value (the struct itself) to the variable s. Then a pointer to that struct may be assigned to another variable (p2 in the following example).

s := StructName{}
p2 := &s

answered Nov 8, 2015 at 14:33

John

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1 Comment

linirod Over a year ago

Thanks for your quick reply however that's not my problem. I updated the question.

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