Tip: Use the go playground at play.golang.org to post code.

The reason why you can't use a String() method with a pointer receiver is
because when passed to Println, it is stored in an interface, and you can't
get the address of a value stored in an interface to call the method.

Here are an in-depth set of examples: http://play.golang.org/p/uQL_RMJ_Bj

The efficiency of passing a 24-byte struct by value vs. a pointer (8-bytes)
isn't that big an issue several reasons.

    1. To access the fields in the method, you must dereference the pointer,
    so the pointer method could in fact be slower in some situations.
    2. Copies are very cheap for small values
    3. If the function/method is inlined, the copy could be elided by the
    4. If the function/method is not inlined, the copy is likely
    insignificant compared to the cost of calling the function/method.

This doesn't mean that you should never use pointer receivers:

    1. You can't modify the original object with a value receiver (copy gets
    modified instead)
    2. If there is only supposed to be conceptually one instance of the
    object (eg: a counter or lock), then you shouldn't use a value receiver,
    often due to #1
    3. For large types, especially in the case of simple methods, the copy
    cost is likely a significant part of the total method cost
    4. It usually a good idea to have all the methods following a single
    style, either all pointer receivers or all value receivers

On Sunday, December 7, 2014 5:53:49 PM UTC-8, hus...@163.com wrote:

Why Golang decides the "Sting()" argument is actually a copy but not the reference?

package main

import "fmt"

type Student struct {

name string

age int


func (s Student) String() string {

fmt.Printf("%p\n", &s) //It shows that the s is actually a copy, if the function is declared as "func (s *Stude///nt) String() string" then it will not be called

return fmt.Sprintf("name is %s\n", s.name)


func main() {

s := Student{name: "charlie", age: 18}

fmt.Printf("%p\n", &s)






name is charlie

as it shows, the argument passing to String() is actual a copy of the object, is that a waste of efficiency?
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