On Tue, Aug 10, 2021 at 3:50 PM E Z <legend...@gmail.com> wrote:
> It works when I changed the code as your suggested. That's great, thanks.
>
> And I'm still a little confused here, you know when we use the struct
> method directly, it is only when the function is called that the type of
> receiver determines whether the passed struct is a pointer or a copied
> value. But when using a function pointer, why does it decide whether to
> bind a pointer or a copied value at the time of assignment, but not at the
> time of function called?
>
> It seems that these two behaviors are not consistent. Is there any benefit
> to doing so? I didn't find much information on this topic on Google. Is
> there any extended reading on this topic?
>
It is consistent. The pointer to function assignment captures the current
receiver.
func (z Zoo) Display()
func (z *Zoo) DisplayPtr()
fptr:=gz.Display --> Captures gz, since Display gets gz by value, captures
gz by value
fptr2:= gz.DisplayPtr -> Captures gz, since DisplayPtr gets gz by
reference, captures *gz
That is:
gz:=&Zoo{}
fptr2:=gz.DisplayPtr
gz=&Zoo{}
fptr2() -> This will call the DisplayPtr with the first value of gz, not
the second
>
> On Tuesday, August 10, 2021 at 12:07:26 PM UTC-7 bse...@computer.org
> wrote:
>
>> On Tue, Aug 10, 2021 at 12:01 PM E Z <lege...@gmail.com> wrote:
>>
>>> I feel confused when I use the function pointer which point to the
>>> struct method. Here is the test code:
>>>
>>> /***
>>> package main
>>>
>>> type Zoo struct {
>>> Animal string
>>> }
>>>
>>> func (z Zoo) Display(){
>>> fmt.Printf("Current animal is:%s\n", z.Animal)
>>> }
>>>
>>
>> This method has a value receiver. When pf is assigned to gz.Display, it
>> is assigned with its receiver, which is a copy of gz.
>>
>> Change the method to func (z *Zoo) Display(), and it will work as you
>> expect.
>>
>>
>>>
>>> func main(){
>>> gz := &Zoo{
>>> Animal: "Monkey",
>>> }
>>>
>>> pf := gz.Display
>>> pf() //display "Current animal
>>> is Monkey"
>>> gz.Animal="Tiger"
>>> pf() //display "Current
>>> animal is Monkey"
>>> gz.Display() //display "Current animal is
>>> Tiger"
>>> }
>>> ***/
>>> As the code is shown above, even though I changed the value of the
>>> member field of the Zoo instance gz, the function pointer call that
>>> followed still prints the unmodified value.
>>>
>>> Can someone help explain why? In my opinion, The function pointer pf
>>> should bind to the instance gz and its method(note that gz here is a
>>> pointer variable), if so anytime I change the value of the variable gz,
>>> pf should reflect the changes.
>>>
>>> Thanks,
>>> Ethan
>>>
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>>>
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