Re: [go-nuts] some incorrect code in blog.

[Brian Candler]

Ergh. Thank you for putting me right.

That is definitely a good reason for avoiding *named* return values 
completely.

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Re: [go-nuts] some incorrect code in blog.

['Axel Wagner' via golang-nuts]

On Sat, Nov 27, 2021 at 11:03 AM Brian Candler  wrote:

> Whether (1) or (2) applies depends whether the final return is a "naked"
> one or not.  In this case it isn't:
>
>
> *return io.Copy(dst, src)*
>
> Therefore, the value returned is whatever io.Copy() returns
>

That is not true .

FWIW I think the code in the blog post is bad, as it doesn't check the
errors from `Close`. But a) it's an old post, I don't know if it's worth
fixing it and b) fixing it might distort the point - teaching the mechanics
of defer.

The best way to fix it would probably be to do `return written,
dst.Close()` - i.e. call `Close()` twice.


> There is a wider question as to whether you should check the error return
> from Close() in the first place.  In some rare cases it *might* show
> something, e.g. Close() when you are *writing* a file may return disk full
> errors for some filesystems.  However it doesn't give a guarantee that all
> errors are caught.
>
> If you need to guarantee that the data was successfully written to disk
> then you should call Fsync() and check the return value of that, but that's
> an expensive operation (it forces the OS to write dirty buffers to disk).
> Even then there are issues to beware of, especially if multiple threads are
> calling Fsync() on the same file.  See
> https://www.youtube.com/watch?v=74c19hwY2oE
> https://wiki.postgresql.org/wiki/Fsync_Errors
> # both linked from: https://docs.ceph.com/en/mimic/cephfs/posix/
>
> Most applications don't need this type of guarantee, i.e. if the disk
> becomes full or there are I/O errors then they accept that the data on disk
> will be corrupt.
>
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> 
> .
>

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Re: [go-nuts] some incorrect code in blog.

[Brian Candler]

On Saturday, 27 November 2021 at 07:55:10 UTC tapi...@gmail.com wrote:

> Isn't the code should be:
>
> *func CopyFile() {*
> *   ...*
> *   if err != nil {*
> *  return*
> *   }*
>
> *   defer func() { err = src.Close() }()*
> *   ...*
> *}*
>

No.

Note that the signature of this function (from the original blog post) is:

*func CopyFile(dstName, srcName string) (written int64, err error) {*

Given that, I think that your proposed change is a bad idea. Either:
(1) it may mask the real return error value.  For example, if err was set 
to a non-nil value, but the Close() is successful, err will be set back to 
nil
Or:
(2) it will make no difference at all.

Whether (1) or (2) applies depends whether the final return is a "naked" 
one or not.  In this case it isn't:


*return io.Copy(dst, src)*

Therefore, the value returned is whatever io.Copy() returns, so setting 
"err" in the defer statement makes no difference at all.  Your version of 
the code is more confusing, because it implies that it does something which 
it doesn't.
 
There is a wider question as to whether you should check the error return 
from Close() in the first place.  In some rare cases it *might* show 
something, e.g. Close() when you are *writing* a file may return disk full 
errors for some filesystems.  However it doesn't give a guarantee that all 
errors are caught.

If you need to guarantee that the data was successfully written to disk 
then you should call Fsync() and check the return value of that, but that's 
an expensive operation (it forces the OS to write dirty buffers to disk). 
Even then there are issues to beware of, especially if multiple threads are 
calling Fsync() on the same file.  See
https://www.youtube.com/watch?v=74c19hwY2oE
https://wiki.postgresql.org/wiki/Fsync_Errors
# both linked from: https://docs.ceph.com/en/mimic/cephfs/posix/

Most applications don't need this type of guarantee, i.e. if the disk 
becomes full or there are I/O errors then they accept that the data on disk 
will be corrupt.

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Re: [go-nuts] some incorrect code in blog.

[tapi...@gmail.com]

Isn't the code should be:

*func CopyFile() {*
*   ...*
*   if err != nil {*
*  return*
*   }*

*   defer func() { err = src.Close() }()*
*   ...*
*}*

On Thursday, November 25, 2021 at 12:18:20 PM UTC+8 Ian Lance Taylor wrote:

> On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang  wrote:
> >
> > There is some incorrect code in 
> https://go.dev/blog/defer-panic-and-recover blog.
> >
> > The original code is
> > func CopyFile() {
> > ...
> > if err != nil {
> > return
> > }
> > defer src.Close()
> > ...
> > }
> >
> > I think the correct code should be
> > func CopyFile() {
> > ...
> > defer src.Close()
> > if err != nil {
> > return
> > }
> > ...
> > }
> >
> > I do not know how to modify the go blog, can anyone help? Thank you.
>
> If you want to update the blog, send a patch for
> golang.org/x/website/_content/blog.
>
> (But please don't send this particular change. As Kurtis noted, the
> existing code is correct, and your change would not be correct.
> Thanks.)
>
> Ian
>

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Re: [go-nuts] some incorrect code in blog.

[Roland Müller]

Hello David,

the behavior of File.Close() on nil was a surprise for me too.

Obviously, even just calling a "methods" of some struct instance that is
not initialized succeeds in Go. A panic occurs only when the program tries
to derefer nil pointer:

'func (ev *Event) do()' only uses the pointer but does not derefer it.
Thus, no panic.

Here 'func (ev Event) do2()' derefers nil pointer already before call.
Panic in main.main()

https://go.dev/play/p/O_C0RpXb46h

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x47f812]

goroutine 1 [running]:
main.main()
/tmp/sandbox1681946220/prog.go:14 +0x112


Here 'func (ev *Event) getS()' derefers the pointer. Panic happens inside
the main.getS()
https://go.dev/play/p/lto_JSFC2Qd

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x47f8d4]

goroutine 1 [running]:
main.(*Event).getS(0x4b2a40)
/tmp/sandbox1571083836/prog.go:35 +0x14


BR,

Roland



Am Do., 25. Nov. 2021 um 22:54 Uhr schrieb David Karr <
davidmichaelk...@gmail.com>:

> I meant, did you test it with a bad path, and with the defer before the
> error check?  I believe you implied that this didn't result in a failure.
> It would have happened on exit from the method, if anything.
>
> On Thu, Nov 25, 2021 at 12:49 PM Roland Müller  wrote:
>
>> Yes. Actually I only tested with a non-existing file.
>>
>> But if you mean that case were also the directory is missing: behavior is
>> still the same.
>>
>> BR,
>> Roland
>>
>> func main() {
>> f, err := os.Open("/tmp/dat_is_net_do/dat")
>> //defer f.Close()
>> fmt.Printf("%v\n", f)
>> if err != nil {
>>   fmt.Println("NO FILE")
>>   //return
>>}
>>defer f.Close()
>>fmt.Println("END")
>> }
>>
>>
>> Am Do., 25. Nov. 2021 um 21:43 Uhr schrieb David Karr <
>> davidmichaelk...@gmail.com>:
>>
>>> And did you test that with a file path that would fail?
>>>
>>> On Thu, Nov 25, 2021, 11:40 Roland Müller  wrote:
>>>
>>>> Hello,
>>>>
>>>> actually trying this with os.Open() the program behaves the same
>>>> regardless whether the defer is before or after the error handling, Thus,
>>>> no panic :-)
>>>>
>>>> Isn't anything declared with defer always running after the user code
>>>> in the given func ends? I am too tired now to look this up.
>>>>
>>>> BR,
>>>>
>>>> Roland
>>>>
>>>> package main
>>>>
>>>> import (
>>>> "fmt"
>>>> "os"
>>>> )
>>>>
>>>> func main() {
>>>> f, err := os.Open("/tmp/dat")
>>>> //defer f.Close()
>>>> fmt.Printf("%v\n", f)
>>>> if err != nil {
>>>>   fmt.Println("NO FILE")
>>>>   //return
>>>>}
>>>>defer f.Close()
>>>>fmt.Println("END")
>>>> }
>>>>
>>>> Output:
>>>> 
>>>> NO FILE
>>>> END
>>>>
>>>>
>>>> On 11/25/21 10:19, Fannie Zhang wrote:
>>>>
>>>> OK, I see. Thank you.
>>>>
>>>>
>>>>
>>>> *From:* Kurtis Rader  
>>>> *Sent:* Thursday, November 25, 2021 10:26 AM
>>>> *To:* Fannie Zhang  
>>>> *Cc:* golang-nuts 
>>>> 
>>>> *Subject:* Re: [go-nuts] some incorrect code in blog.
>>>>
>>>>
>>>>
>>>> Notice the date of that blog article: 2010-08-04. It's more than eleven
>>>> years old. Blog articles are not updated as the language changes. However,
>>>> in this case the example in that article is correct. If `os.Open()` returns
>>>> an error then the `src` return value is invalid.
>>>>
>>>>
>>>>
>>>> On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang 
>>>> wrote:
>>>>
>>>> Hi all,
>>>>
>>>>
>>>>
>>>> There is some incorrect code in
>>>> https://go.dev/blog/defer-panic-and-recover blog.
>>>>
>>>>
>>>>
>>>> The original code is
>>>>
>>>> *func CopyFile() {*
>>>>
>>>> *   ...*
&g

Re: [go-nuts] some incorrect code in blog.

[David Karr]

I meant, did you test it with a bad path, and with the defer before the
error check?  I believe you implied that this didn't result in a failure.
It would have happened on exit from the method, if anything.

On Thu, Nov 25, 2021 at 12:49 PM Roland Müller  wrote:

> Yes. Actually I only tested with a non-existing file.
>
> But if you mean that case were also the directory is missing: behavior is
> still the same.
>
> BR,
> Roland
>
> func main() {
> f, err := os.Open("/tmp/dat_is_net_do/dat")
> //defer f.Close()
> fmt.Printf("%v\n", f)
> if err != nil {
>   fmt.Println("NO FILE")
>   //return
>}
>defer f.Close()
>fmt.Println("END")
> }
>
>
> Am Do., 25. Nov. 2021 um 21:43 Uhr schrieb David Karr <
> davidmichaelk...@gmail.com>:
>
>> And did you test that with a file path that would fail?
>>
>> On Thu, Nov 25, 2021, 11:40 Roland Müller  wrote:
>>
>>> Hello,
>>>
>>> actually trying this with os.Open() the program behaves the same
>>> regardless whether the defer is before or after the error handling, Thus,
>>> no panic :-)
>>>
>>> Isn't anything declared with defer always running after the user code in
>>> the given func ends? I am too tired now to look this up.
>>>
>>> BR,
>>>
>>> Roland
>>>
>>> package main
>>>
>>> import (
>>> "fmt"
>>> "os"
>>> )
>>>
>>> func main() {
>>> f, err := os.Open("/tmp/dat")
>>> //defer f.Close()
>>> fmt.Printf("%v\n", f)
>>> if err != nil {
>>>       fmt.Println("NO FILE")
>>>   //return
>>>}
>>>defer f.Close()
>>>fmt.Println("END")
>>> }
>>>
>>> Output:
>>> 
>>> NO FILE
>>> END
>>>
>>>
>>> On 11/25/21 10:19, Fannie Zhang wrote:
>>>
>>> OK, I see. Thank you.
>>>
>>>
>>>
>>> *From:* Kurtis Rader  
>>> *Sent:* Thursday, November 25, 2021 10:26 AM
>>> *To:* Fannie Zhang  
>>> *Cc:* golang-nuts 
>>> 
>>> *Subject:* Re: [go-nuts] some incorrect code in blog.
>>>
>>>
>>>
>>> Notice the date of that blog article: 2010-08-04. It's more than eleven
>>> years old. Blog articles are not updated as the language changes. However,
>>> in this case the example in that article is correct. If `os.Open()` returns
>>> an error then the `src` return value is invalid.
>>>
>>>
>>>
>>> On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang 
>>> wrote:
>>>
>>> Hi all,
>>>
>>>
>>>
>>> There is some incorrect code in
>>> https://go.dev/blog/defer-panic-and-recover blog.
>>>
>>>
>>>
>>> The original code is
>>>
>>> *func CopyFile() {*
>>>
>>> *   ...*
>>>
>>> *   if err != nil {*
>>>
>>> *  return*
>>>
>>> *   }*
>>>
>>> *   defer src.Close()*
>>>
>>> *   ...*
>>>
>>> *}*
>>>
>>>
>>>
>>> I think the correct code should be
>>>
>>> *func CopyFile() {*
>>>
>>> *   ...*
>>>
>>> *   defer src.Close()*
>>>
>>> *   if err != nil {*
>>>
>>> *  return*
>>>
>>> *   }*
>>>
>>> *   ...*
>>>
>>> *}*
>>>
>>>
>>>
>>> I do not know how to modify the go blog, can anyone help? Thank you.
>>>
>>>
>>>
>>> Best regards,
>>>
>>> Fannie Zhang
>>>
>>> --
>>> You received this message because you are subscribed to the Google
>>> Groups "golang-nuts" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to golang-nuts+unsubscr...@googlegroups.com.
>>> To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/golang-nuts/726e95ed-9b14-46a5-bb09-7821616f4ff9n%40googlegroups.com
>>> <https://groups.google.com/d/msgid/golang-nuts/726e95ed-9b14-46a5-bb09-7821616f4ff9n%40googlegroups.com?utm_medium=email_source=footer>
>>> .
>>>
>>>
>>>
>>>
>>> --
>>>
>>> Kurtis Rader
>>>

Re: [go-nuts] some incorrect code in blog.

[Roland Müller]

Yes. Actually I only tested with a non-existing file.

But if you mean that case were also the directory is missing: behavior is
still the same.

BR,
Roland

func main() {
f, err := os.Open("/tmp/dat_is_net_do/dat")
//defer f.Close()
fmt.Printf("%v\n", f)
if err != nil {
  fmt.Println("NO FILE")
  //return
   }
   defer f.Close()
   fmt.Println("END")
}


Am Do., 25. Nov. 2021 um 21:43 Uhr schrieb David Karr <
davidmichaelk...@gmail.com>:

> And did you test that with a file path that would fail?
>
> On Thu, Nov 25, 2021, 11:40 Roland Müller  wrote:
>
>> Hello,
>>
>> actually trying this with os.Open() the program behaves the same
>> regardless whether the defer is before or after the error handling, Thus,
>> no panic :-)
>>
>> Isn't anything declared with defer always running after the user code in
>> the given func ends? I am too tired now to look this up.
>>
>> BR,
>>
>> Roland
>>
>> package main
>>
>> import (
>> "fmt"
>> "os"
>> )
>>
>> func main() {
>> f, err := os.Open("/tmp/dat")
>> //defer f.Close()
>> fmt.Printf("%v\n", f)
>> if err != nil {
>>   fmt.Println("NO FILE")
>>   //return
>>}
>>defer f.Close()
>>fmt.Println("END")
>> }
>>
>> Output:
>> 
>> NO FILE
>> END
>>
>>
>> On 11/25/21 10:19, Fannie Zhang wrote:
>>
>> OK, I see. Thank you.
>>
>>
>>
>> *From:* Kurtis Rader  
>> *Sent:* Thursday, November 25, 2021 10:26 AM
>> *To:* Fannie Zhang  
>> *Cc:* golang-nuts 
>> 
>> *Subject:* Re: [go-nuts] some incorrect code in blog.
>>
>>
>>
>> Notice the date of that blog article: 2010-08-04. It's more than eleven
>> years old. Blog articles are not updated as the language changes. However,
>> in this case the example in that article is correct. If `os.Open()` returns
>> an error then the `src` return value is invalid.
>>
>>
>>
>> On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang 
>> wrote:
>>
>> Hi all,
>>
>>
>>
>> There is some incorrect code in
>> https://go.dev/blog/defer-panic-and-recover blog.
>>
>>
>>
>> The original code is
>>
>> *func CopyFile() {*
>>
>> *   ...*
>>
>> *   if err != nil {*
>>
>> *  return*
>>
>> *   }*
>>
>> *   defer src.Close()*
>>
>> *   ...*
>>
>> *}*
>>
>>
>>
>> I think the correct code should be
>>
>> *func CopyFile() {*
>>
>> *   ...*
>>
>> *   defer src.Close()*
>>
>> *   if err != nil {*
>>
>> *  return*
>>
>> *   }*
>>
>> *   ...*
>>
>> *}*
>>
>>
>>
>> I do not know how to modify the go blog, can anyone help? Thank you.
>>
>>
>>
>> Best regards,
>>
>> Fannie Zhang
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "golang-nuts" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to golang-nuts+unsubscr...@googlegroups.com.
>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/golang-nuts/726e95ed-9b14-46a5-bb09-7821616f4ff9n%40googlegroups.com
>> <https://groups.google.com/d/msgid/golang-nuts/726e95ed-9b14-46a5-bb09-7821616f4ff9n%40googlegroups.com?utm_medium=email_source=footer>
>> .
>>
>>
>>
>>
>> --
>>
>> Kurtis Rader
>>
>> Caretaker of the exceptional canines Junior and Hank
>> IMPORTANT NOTICE: The contents of this email and any attachments are
>> confidential and may also be privileged. If you are not the intended
>> recipient, please notify the sender immediately and do not disclose the
>> contents to any other person, use it for any purpose, or store or copy the
>> information in any medium. Thank you. --
>> You received this message because you are subscribed to the Google Groups
>> "golang-nuts" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to golang-nuts+unsubscr...@googlegroups.com.
>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/golang-nuts/PAXPR08MB6640963981E13AC180B4E19594629%40PAXPR08MB6640.eurprd08.prod.outlook.com
>> <https://groups.google.com/d/msgid/golang-nuts/PAXPR08MB6640963981E13AC180B4E19594629%40PAXPR08MB6640.eurprd08.prod.outlook.com?utm_medium=email_source=footer>
>> .
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "golang-nuts" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to golang-nuts+unsubscr...@googlegroups.com.
>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/golang-nuts/4d0b379f-c2a0-a314-e2d3-5fec36528845%40gmail.com
>> <https://groups.google.com/d/msgid/golang-nuts/4d0b379f-c2a0-a314-e2d3-5fec36528845%40gmail.com?utm_medium=email_source=footer>
>> .
>>
>

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Re: [go-nuts] some incorrect code in blog.

[David Karr]

And did you test that with a file path that would fail?

On Thu, Nov 25, 2021, 11:40 Roland Müller  wrote:

> Hello,
>
> actually trying this with os.Open() the program behaves the same
> regardless whether the defer is before or after the error handling, Thus,
> no panic :-)
>
> Isn't anything declared with defer always running after the user code in
> the given func ends? I am too tired now to look this up.
>
> BR,
>
> Roland
>
> package main
>
> import (
> "fmt"
> "os"
> )
>
> func main() {
> f, err := os.Open("/tmp/dat")
> //defer f.Close()
> fmt.Printf("%v\n", f)
> if err != nil {
>   fmt.Println("NO FILE")
>   //return
>}
>defer f.Close()
>fmt.Println("END")
> }
>
> Output:
> 
> NO FILE
> END
>
>
> On 11/25/21 10:19, Fannie Zhang wrote:
>
> OK, I see. Thank you.
>
>
>
> *From:* Kurtis Rader  
> *Sent:* Thursday, November 25, 2021 10:26 AM
> *To:* Fannie Zhang  
> *Cc:* golang-nuts 
> 
> *Subject:* Re: [go-nuts] some incorrect code in blog.
>
>
>
> Notice the date of that blog article: 2010-08-04. It's more than eleven
> years old. Blog articles are not updated as the language changes. However,
> in this case the example in that article is correct. If `os.Open()` returns
> an error then the `src` return value is invalid.
>
>
>
> On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang  wrote:
>
> Hi all,
>
>
>
> There is some incorrect code in
> https://go.dev/blog/defer-panic-and-recover blog.
>
>
>
> The original code is
>
> *func CopyFile() {*
>
> *   ...*
>
> *   if err != nil {*
>
> *  return*
>
> *   }*
>
> *   defer src.Close()*
>
> *   ...*
>
> *}*
>
>
>
> I think the correct code should be
>
> *func CopyFile() {*
>
> *   ...*
>
> *   defer src.Close()*
>
> *   if err != nil {*
>
> *  return*
>
> *   }*
>
> *   ...*
>
> *}*
>
>
>
> I do not know how to modify the go blog, can anyone help? Thank you.
>
>
>
> Best regards,
>
> Fannie Zhang
>
> --
> You received this message because you are subscribed to the Google Groups
> "golang-nuts" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to golang-nuts+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/golang-nuts/726e95ed-9b14-46a5-bb09-7821616f4ff9n%40googlegroups.com
> <https://groups.google.com/d/msgid/golang-nuts/726e95ed-9b14-46a5-bb09-7821616f4ff9n%40googlegroups.com?utm_medium=email_source=footer>
> .
>
>
>
>
> --
>
> Kurtis Rader
>
> Caretaker of the exceptional canines Junior and Hank
> IMPORTANT NOTICE: The contents of this email and any attachments are
> confidential and may also be privileged. If you are not the intended
> recipient, please notify the sender immediately and do not disclose the
> contents to any other person, use it for any purpose, or store or copy the
> information in any medium. Thank you. --
> You received this message because you are subscribed to the Google Groups
> "golang-nuts" group.
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Re: [go-nuts] some incorrect code in blog.

[Roland Müller]

Hello,

actually trying this with os.Open() the program behaves the same 
regardless whether the defer is before or after the error handling, 
Thus, no panic :-)


Isn't anything declared with defer always running after the user code in 
the given func ends? I am too tired now to look this up.


BR,

Roland

package main

import (
    "fmt"
    "os"
)

func main() {
    f, err := os.Open("/tmp/dat")
    //defer f.Close()
    fmt.Printf("%v\n", f)
    if err != nil {
  fmt.Println("NO FILE")
  //return
   }
   defer f.Close()
   fmt.Println("END")
}

Output:


NO FILE
END


On 11/25/21 10:19, Fannie Zhang wrote:


OK, I see. Thank you.

*From:* Kurtis Rader 
*Sent:* Thursday, November 25, 2021 10:26 AM
*To:* Fannie Zhang 
*Cc:* golang-nuts 
*Subject:* Re: [go-nuts] some incorrect code in blog.

Notice the date of that blog article: 2010-08-04. It's more than 
eleven years old. Blog articles are not updated as the language 
changes. However, in this case the example in that article is correct. 
If `os.Open()` returns an error then the `src` return value is invalid.


On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang  wrote:

Hi all,

There is some incorrect code in
https://go.dev/blog/defer-panic-and-recover blog.

The original code is

/func CopyFile() {/

/   .../

/   if err != nil {/

/      return/

/   }/

/   defer src.Close()/

/   .../

/}/

I think the correct code should be

/func CopyFile() {/

/   .../

/   defer src.Close()/

/   if err != nil {/

/      return/

/   }/

/   .../

/}/

I do not know how to modify the go blog, can anyone help? Thank you.

Best regards,

Fannie Zhang

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RE: [go-nuts] some incorrect code in blog.

[Fannie Zhang]

OK, I see. Thank you.

From: Kurtis Rader 
Sent: Thursday, November 25, 2021 10:26 AM
To: Fannie Zhang 
Cc: golang-nuts 
Subject: Re: [go-nuts] some incorrect code in blog.

Notice the date of that blog article: 2010-08-04. It's more than eleven years 
old. Blog articles are not updated as the language changes. However, in this 
case the example in that article is correct. If `os.Open()` returns an error 
then the `src` return value is invalid.

On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang 
mailto:fannie.zh...@arm.com>> wrote:
Hi all,

There is some incorrect code in https://go.dev/blog/defer-panic-and-recover 
blog.

The original code is
func CopyFile() {
   ...
   if err != nil {
  return
   }
   defer src.Close()
   ...
}

I think the correct code should be
func CopyFile() {
   ...
   defer src.Close()
   if err != nil {
  return
   }
   ...
}

I do not know how to modify the go blog, can anyone help? Thank you.

Best regards,
Fannie Zhang
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IMPORTANT NOTICE: The contents of this email and any attachments are 
confidential and may also be privileged. If you are not the intended recipient, 
please notify the sender immediately and do not disclose the contents to any 
other person, use it for any purpose, or store or copy the information in any 
medium. Thank you.

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Re: [go-nuts] some incorrect code in blog.

[David Karr]

On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang  wrote:

> Hi all,
>
> There is some incorrect code in
> https://go.dev/blog/defer-panic-and-recover blog.
>
> The original code is
> *func CopyFile() {*
> *   ...*
> *   if err != nil {*
> *  return*
> *   }*
> *   defer src.Close()*
> *   ...*
> *}*
>
> I think the correct code should be
> *func CopyFile() {*
> *   ...*
> *   defer src.Close()*
> *   if err != nil {*
> *  return*
> *   }*
> *   ...*
> *}*
>
> I do not know how to modify the go blog, can anyone help? Thank you.
>

Well, I would call myself a Go newbie, but I would think that if err !=
nil, that means there was an error, so the value of "src" would be either
invalid or nil, so putting the "defer" before the err check would possibly
result in a panic. I'd say the original code is correct.


> Best regards,
> Fannie Zhang
>
> --
> You received this message because you are subscribed to the Google Groups
> "golang-nuts" group.
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> email to golang-nuts+unsubscr...@googlegroups.com.
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> 
> .
>

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Re: [go-nuts] some incorrect code in blog.

[Ian Lance Taylor]

On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang  wrote:
>
> There is some incorrect code in https://go.dev/blog/defer-panic-and-recover 
> blog.
>
> The original code is
> func CopyFile() {
>...
>if err != nil {
>   return
>}
>defer src.Close()
>...
> }
>
> I think the correct code should be
> func CopyFile() {
>...
>defer src.Close()
>if err != nil {
>   return
>}
>...
> }
>
> I do not know how to modify the go blog, can anyone help? Thank you.

If you want to update the blog, send a patch for
golang.org/x/website/_content/blog.

(But please don't send this particular change.  As Kurtis noted, the
existing code is correct, and your change would not be correct.
Thanks.)

Ian

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Re: [go-nuts] some incorrect code in blog.

[Leam Hall]

On 11/24/21 20:26, Kurtis Rader wrote:

Notice the date of that blog article: 2010-08-04. It's more than eleven years 
old. Blog articles are not updated as the language changes.


It might be good to resolve that. If the authoritative info source for the 
language makes a habit of keeping old data up front, either update the material 
or quit posting stuff that ages to incorrectness. Winning a 2010 award ages 
well, code from 2010 might not. New community members don't need the hindrance, 
do they?

Leam

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Re: [go-nuts] some incorrect code in blog.

[Kurtis Rader]

Notice the date of that blog article: 2010-08-04. It's more than eleven
years old. Blog articles are not updated as the language changes. However,
in this case the example in that article is correct. If `os.Open()` returns
an error then the `src` return value is invalid.

On Wed, Nov 24, 2021 at 6:14 PM Fannie Zhang  wrote:

> Hi all,
>
> There is some incorrect code in
> https://go.dev/blog/defer-panic-and-recover blog.
>
> The original code is
> *func CopyFile() {*
> *   ...*
> *   if err != nil {*
> *  return*
> *   }*
> *   defer src.Close()*
> *   ...*
> *}*
>
> I think the correct code should be
> *func CopyFile() {*
> *   ...*
> *   defer src.Close()*
> *   if err != nil {*
> *  return*
> *   }*
> *   ...*
> *}*
>
> I do not know how to modify the go blog, can anyone help? Thank you.
>
> Best regards,
> Fannie Zhang
>
> --
> You received this message because you are subscribed to the Google Groups
> "golang-nuts" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to golang-nuts+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/golang-nuts/726e95ed-9b14-46a5-bb09-7821616f4ff9n%40googlegroups.com
> 
> .
>


-- 
Kurtis Rader
Caretaker of the exceptional canines Junior and Hank

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[go-nuts] some incorrect code in blog.

[Fannie Zhang]

Hi all,

There is some incorrect code in https://go.dev/blog/defer-panic-and-recover 
blog.

The original code is
*func CopyFile() {*
*   ...*
*   if err != nil {*
*  return*
*   }*
*   defer src.Close()*
*   ...*
*}*

I think the correct code should be
*func CopyFile() {*
*   ...*
*   defer src.Close()*
*   if err != nil {*
*  return*
*   }*
*   ...*
*}*

I do not know how to modify the go blog, can anyone help? Thank you.

Best regards,
Fannie Zhang

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