First of all, thanks for all the answers. A standard use case in Python is
to use with the a closing context manager which will just call close on a
given object. That one could be easily done with a defer statement.
However, coming from Java lately, retrieving a DB-connection from a pool,
opening a transaction and committing/aborting and returningafterwards seems
something which could be handled with such a construct. How would you do
this in Golang?
Am Mittwoch, 12. September 2018 15:37:12 UTC+2 schrieb Robert Engels:
>
> Agree it can be done - not sure I would want to maintain that in a large
> system as you are paying the LOC penalty at every call site. Seems easier
> to just add the context callback in the methods themselves so then you are
> in control of the code penalty.
>
> On Sep 12, 2018, at 8:17 AM, Sebastien Binet <bi...@cern.ch <javascript:>>
> wrote:
>
>
>
> On Wed, Sep 12, 2018 at 2:55 PM robert engels <ren...@ix.netcom.com
> <javascript:>> wrote:
>
>> Ok, now the coffee has kicked in, and it still has problems, because you
>> cannot call a method and use a return value other than error without
>> multiple signatures, unless you move all of the return values outside of
>> the closure - like his example does with var a.
>>
>
>> This would be extremely tedious (and probably error prone) to use IMO,
>> especially with Go’s multiple return values.
>>
>
> one has to be careful, yes. but it's not completely out of reach.
>
> func Foo(a, b int) (int, error) { ... }
>
> func Do() {
> var out = 0
> With(ctx, func() error {
> var err error
> out, err = Foo(42, 66)
> return err
> })
> }
>
> closures are great! (like fezzes and bowties, actually :P)
>
> -s
>
>
>>
>> On Sep 12, 2018, at 7:50 AM, robert engels <ren...@ix.netcom.com
>> <javascript:>> wrote:
>>
>> Too early, and the coffee had not kicked in...
>>
>> On Sep 12, 2018, at 7:49 AM, robert engels <ren...@ix.netcom.com
>> <javascript:>> wrote:
>>
>> Yes, you are correct. My bad :)
>>
>> On Sep 12, 2018, at 7:34 AM, Sebastien Binet <bi...@cern.ch <javascript:>>
>> wrote:
>>
>>
>>
>> On Wed, Sep 12, 2018 at 2:23 PM robert engels <ren...@ix.netcom.com
>> <javascript:>> wrote:
>>
>>> I am pretty sure that is not correct, I am referring to:
>>>
>>> func WithContext(context Context, f func() error) error {
>>> context.__entry__()
>>> defer context.__exit__()
>>> return f()
>>> }
>>>
>>>
>>> You will need a lot of WithContext methods - based on the different
>>> signatures of function f.
>>>
>>> See the main method… I am assuming this is attempting to be a general
>>> facility - and thus the signature of f will vary.
>>>
>>
>> you just need to wrap it with a closure, just as Eric did:
>>
>> e.g.:
>> func QueryDB(a,b int) error { ... }
>>
>> WithContext(ctx, func() error {
>> return QueryDB(42, 666)
>> })
>>
>> and voila.
>>
>> -s
>>
>>
>>
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>>
>>
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