Duh, sorry for the spam - I was reading the text without looking at the code.
Makes perfect sense.
-----Original Message-----
>From: Robert Engels <reng...@ix.netcom.com>
>Sent: Nov 20, 2019 2:31 PM
>To: Robert Engels <reng...@ix.netcom.com>, Ian Lance Taylor <i...@golang.org>,
>Orson Cart <objectivedynam...@gmail.com>
>Cc: golang-nuts <golang-nuts@googlegroups.com>
>Subject: Re: [go-nuts] Difference with function returning struct and function
>returning pointer to struct
>
>I must of misread something, because this code works fine:
>
>package main
>
>import "fmt"
>
>type X struct {
> x int
>}
>
>func getX() X {
> var x X
> return x
>}
>
>func main() {
> c := getX()
> c.x = 1
> fmt.Println(c)
>}
>
>and is what I would expect to happen. Why is this not the same behavior in the
>other code?
>
>
>
>
>
>-----Original Message-----
>>From: Robert Engels <reng...@ix.netcom.com>
>>Sent: Nov 20, 2019 2:25 PM
>>To: Ian Lance Taylor <i...@golang.org>, Orson Cart
>><objectivedynam...@gmail.com>
>>Cc: golang-nuts <golang-nuts@googlegroups.com>
>>Subject: Re: [go-nuts] Difference with function returning struct and function
>>returning pointer to struct
>>
>>
>>To be honest, I find this very confusing, especially the statement "Changing
>>a field in that copy won't change anything." because even if I have a copy, I
>>should be able to change the fields, and the changes would be there for the
>>scope, and if I returned the copy, whether by address or copy, the changes
>>would be retained.
>>
>>-----Original Message-----
>>>From: Ian Lance Taylor <i...@golang.org>
>>>Sent: Nov 20, 2019 11:55 AM
>>>To: Orson Cart <objectivedynam...@gmail.com>
>>>Cc: golang-nuts <golang-nuts@googlegroups.com>
>>>Subject: Re: [go-nuts] Difference with function returning struct and
>>>function returning pointer to struct
>>>
>>>On Wed, Nov 20, 2019 at 9:41 AM Orson Cart <objectivedynam...@gmail.com>
>>>wrote:
>>>>
>>>> I'm a newbie to Go having used C and C++ in the past and I'm puzzled about
>>>> something I've just seen.
>>>>
>>>> In the following code getEmployee returns a pointer to a struct. The
>>>> return value is then dereferenced. This code compiles and runs fine:
>>>>
>>>> package main
>>>>
>>>> type employee struct {
>>>> ID int
>>>> name string
>>>> }
>>>>
>>>> var dilbert employee
>>>>
>>>> func main() {
>>>>
>>>> getEmployee().name = "dilbert"
>>>> }
>>>>
>>>> func getEmployee() *employee {
>>>> return &dilbert
>>>> }
>>>>
>>>> However if I modify getEmployee as follows, I get a compilation error:
>>>>
>>>> func getEmployee() employee {
>>>> return dilbert
>>>> }
>>>>
>>>> The error is: cannot assign to getEmployee().name
>>>>
>>>> I assume that it revolves around "assignability" but I'm struggling to
>>>> understand why.
>>>>
>>>> Can anyone tell me why this is?
>>>
>>>There are two kinds of answers.
>>>
>>>One is that the spec only permits setting fields of a struct that is
>>>addressable, and the result of a function call is not addressable.
>>>See https://golang.org/ref/spec#Assignments and
>>>https://golang.org/ref/spec#Address_operators .
>>>
>>>The other kind of answer is that if a function returns a pointer to a
>>>struct, a value of type *employee, then it's normal for that something
>>>else to have a copy of that pointer, perhaps some data structure or
>>>global variable. In your simple example that is the global variable
>>>"dilbert". So it makes sense to permit setting a field of the result
>>>of calling getEmployee(), a value of type *employee, as setting that
>>>field will change the global variable "dilbert". But when
>>>getEmployee() does not return a pointer, but just returns a value of
>>>type "employee", then that is a copy of the value in the global
>>>variable. Changing a field in that copy won't change anything. The
>>>assignment will be made, and then the result will be discarded. Since
>>>that operation is useless, the language does not permit it.
>>>
>>>Ian
>>>
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>>
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