Callback function in Golang

[Peter Hon]

Hi.

  I am using go-couchbase to update data to couchbase, however, I have problem in how to use the callback function.

  The fuction Update require me to pass a callback function in which should be UpdateFunc

  func (b *Bucket) Update(k string, exp int, callback UpdateFunc) error

  So that's what I have done 

  First, I declared a type UpdateFunc:

           type UpdateFunc func(current []byte) (updated []byte, err error)

  Then in the code, I add the following lines:

           fn := UpdateFunc{func(0){}} 

           and then call the Update function:

           bucket.Update("12345",0,fn()}

  But the Go says the following error:

                          syntax error: unexpected literal 0, expecting ) for this line fn := UpdateFunc{func(0) { } }

    So what I am doing wrong? So how can I make the callback function work ?

Thanks

[Jan Mercl]

On Thu, Aug 14, 2014 at 10:59 AM, Peter Hon <peter...@gmail.com> wrote:
> fn := UpdateFunc{func(0){}}
>
>
> and then call the Update function:
>
>
> bucket.Update("12345",0,fn()}
>
>
>
> But the Go says the following error:
>
>
> syntax error: unexpected literal 0, expecting )
> for this line fn := UpdateFunc{func(0) { } }

I have no idea what is the above supposed to do, but it's definitely
invalid syntax. See http://golang.org/ref/spec#Function_literals

In short, inside the function literal parenthesis, there must be a
list of types ('func(int)' or 'func(string, bool)', ...) or list of
list of names folowed by a type ('func(a int, b, c strin)', ...).

'0' (a numeric literal) is not in those options.

-j

[Francisco Dalla Rosa Soares]

Let's start from the start:

1. Please, avoid the HTML emails, they really hurt in the eye.

2.  You don't have to define the UpdateFunc type by yourself, it's already defined here:

https://github.com/couchbaselabs/go-couchbase/blob/master/client.go#L608

just define the function normally and pass it as an argument or pass an anonymous function as in other languages.

here's a simple example:

http://play.golang.org/p/YOKxRtQqmU

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[Milan P. Stanic]

On Thu, 2014-08-14 at 18:42, Francisco Dalla Rosa Soares wrote:
> Let's start from the start:
>
> 1. Please, avoid the HTML emails, they really hurt in the eye.

What about top-post? Does it hurt?

> 2. You don't have to define the UpdateFunc type by yourself, it's already
> defined here:
> https://github.com/couchbaselabs/go-couchbase/blob/master/client.go#L608
>
> just define the function normally and pass it as an argument or pass an
> anonymous function as in other languages.
> here's a simple example:
> http://play.golang.org/p/YOKxRtQqmU
>
> On Thu, Aug 14, 2014 at 5:59 PM, Peter Hon <peter...@gmail.com> wrote:
> > Hi.
> >
> > I am using go-couchbase to update data to couchbase, however, I have problem in how to use the callback function.

[...]

--
Kind regards, Milan

[James Bardin]

So we can keep our collective time-wasted to a minimum, Peter here seems to cross post everything from StackOverfow

http://stackoverflow.com/questions/25304080/callback-in-golang

[Kevin Powick]

On Thursday, 14 August 2014 16:09:27 UTC+1, mps wrote:

 

What about top-post? Does it hurt?

Not as much as quoting excessive amounts of irrelevant text from the post to which one is replying.

--

Kevin Powick

[Milan P. Stanic]

Dear Kevin,

If you allude to my previous post, I left it by intention to show the
context albeit I trimmed half of the message to which I replied.

N.B. sorry if my English is bad. I'm self taught in English.

--
Kind regards, Milan

[Peter Hon]

I am sorry that I cross post it in stackoverflow. I think there are different people reading in golang-nuts and stackoverflow. And the reponse are different. And I think they are two different sites. If cross post is the problem. I will tried to avoid it in future. Either I will post just one in golang-nuts or stackoverflow. By the way, I am not understand "avoid the HTML emails, they really hurt in the eye". Does it meant the email followed my name?

James Bardin於 2014年8月15日星期五UTC+8上午12時12分34秒寫道：

[James Bardin]

There's no problem posting in both forums to get more feedback, but as was commented on SO, it's polite to link between the two so people aren't duplicating effort. 

[Peter Hon]

Thanks James, you suggestion is nice. By the way, may I know the meaning of  "commented on SO", I am not knowing what is the SO stands for.

[Francisco Dalla Rosa Soares]

So = stack overflow

By HTML Mail hurting the eyes, I meant that you didn't need to use so much formatting in your email.  That it could be simple plain text like your later emails

Best regards 

2014年8月15日金曜日、Peter Hon<peter...@gmail.com>さんは書きました:

Thanks James, you suggestion is nice. By the way, may I know the meaning of  "commented on SO", I am not knowing what is the SO stands for.

--

[Peter Hon]

Thanks all of your suggestion. Now I can run the callback function as follows:

        //defining the function first and passing it as an argument

myfunc := func(current []byte)(updated []byte, err error) {return updated, err }

myb.Update("key123", 1, myfunc)

However, when I run the Update function of the bucket. I checked the couch database. The document with the key of "key123" was disappeared. It seems the Update does not update the value but delete it. What happened?

Thanks