Re: [go-nuts] How to cast *interface{} into *T ?
Thanks guys. I have finished my homework thanks to you:
https://pkg.go.dev/github.com/fairking/di_plus
On Friday, 25 November 2022 at 16:35:50 UTC pattnaik...@gmail.com wrote:
> If you create a wrapper interface type and create *generic constraints* with
> the *MyWrapper* struct then it'll type cast with *interface* with *(T)*.
>
> https://go.dev/play/p/-VnQxG77sDL
>
>
> On Fri, Nov 25, 2022 at 3:38 PM 'Axel Wagner' via golang-nuts <
> golan...@googlegroups.com> wrote:
>
>> If you assign a value to an interface, it will get copied. That's the
>> same as if you assign an int to another int - it will get copied. If you
>> want the interface to contain a reference, you have to assign a pointer to
>> it: https://go.dev/play/p/nLw51pjWh4u
>>
>> Side note: Go doesn't have "instances". It has "variables", which is
>> *probably* what you mean.
>>
>> On Fri, Nov 25, 2022 at 10:55 AM Denis P wrote:
>>
>>> Thank you everyone for your help.
>>> The problem still exists.
>>> I am looking for a solution where s and s2 point to the same instance.
>>> The current example proves they are different instances.
>>> https://go.dev/play/p/_JyfJelhIy4
>>>
>>> The main goal is to store any type in a wrapper and then get the
>>> reference of the actual struct.
>>> Also it must be the same instance, so the println should print 2, 2, 2
>>>
>>> But look like there is no obvious solution. :-(
>>>
>>> On Friday, 25 November 2022 at 08:19:17 UTC Brian Candler wrote:
>>>
>>>> To give a real-world example:
>>>>
>>>> https://pkg.go.dev/github.com/prometheus/client_golang/prometheus
>>>>
>>>> type metrics struct {
>>>> cpuTempprometheus.Gauge
>>>> hdFailures *prometheus.CounterVec
>>>> }
>>>>
>>>> Question: why is prometheus.Gauge not a pointer, but
>>>> *prometheus.CounterVec is a pointer?
>>>>
>>>> Answer: because prometheus.Gauge is an interface, whereas
>>>> prometheus.CounterVec is a struct.
>>>>
>>>> An interface essentially already *contains* a pointer to a data value -
>>>> in fact, a tuple of (type, pointer). So you should never take a pointer
>>>> to
>>>> an interface. Just pass the interface value, and it will copy the (type,
>>>> pointer) pair.
>>>>
>>>> However, when you extract a value from an interface, it *will* always
>>>> copy the internal value. This avoids aliasing issues: someone who passes
>>>> an interface value to someone else, won't expect the recipient to be able
>>>> to change the sender's copy.
>>>>
>>>> e.g.
>>>> https://go.dev/play/p/u5y3Kwm9Ydz
>>>>
>>>> Of course, if your interface *contains* a pointer, then the recipient
>>>> of the interface can modify the thing being pointed to.
>>>> https://go.dev/play/p/o_XAJtNuyGF
>>>>
>>>> But they can't modify the pointer itself held within the interface, to
>>>> make it point to something else.
>>>>
>>>> The short version is: avoid pointers to interfaces, as the FAQ says.
>>>> Instead, let a concrete pointer value satisfy an interface.
>>>>
>>>> On Friday, 25 November 2022 at 07:40:59 UTC Nigel Tao wrote:
>>>>
>>>>> Possibly relevant:
>>>>> https://go.dev/doc/faq#pointer_to_interface
>>>>>
>>>> --
>>> 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...@googlegroups.com.
>>> To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/golang-nuts/948dc8f3-385e-4f50-a44b-ddf4792e6362n%40googlegroups.com
>>>
>>> <https://groups.google.com/d/msgid/golang-nuts/948dc8f3-385e-4f50-a44b-ddf4792e6362n%40googlegroups.com?utm_medium=email&utm_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...@googlegroups.com.
>>
> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/golang-nuts/CAEkBMfE7XX%2BnHJTW36GaoLjQWidY7GCjpHP1zyOJJzMcSq13JA%40mail.gmail.com
>>
>> <https://groups.google.com/d/msgid/golang-nuts/CAEkBMfE7XX%2BnHJTW36GaoLjQWidY7GCjpHP1zyOJJzMcSq13JA%40mail.gmail.com?utm_medium=email&utm_source=footer>
>> .
>>
>
>
> --
>
>
> Thanks & Regards
> Deeptiman Pattnaik
>
--
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/b09312e7-c52e-4517-bed1-1ff0352cabf5n%40googlegroups.com.
Re: [go-nuts] How to cast *interface{} into *T ?
Thank you everyone for your help.
The problem still exists.
I am looking for a solution where s and s2 point to the same instance.
The current example proves they are different instances.
https://go.dev/play/p/_JyfJelhIy4
The main goal is to store any type in a wrapper and then get the reference
of the actual struct.
Also it must be the same instance, so the println should print 2, 2, 2
But look like there is no obvious solution. :-(
On Friday, 25 November 2022 at 08:19:17 UTC Brian Candler wrote:
> To give a real-world example:
>
> https://pkg.go.dev/github.com/prometheus/client_golang/prometheus
>
> type metrics struct {
> cpuTempprometheus.Gauge
> hdFailures *prometheus.CounterVec
> }
>
> Question: why is prometheus.Gauge not a pointer, but
> *prometheus.CounterVec is a pointer?
>
> Answer: because prometheus.Gauge is an interface, whereas
> prometheus.CounterVec is a struct.
>
> An interface essentially already *contains* a pointer to a data value - in
> fact, a tuple of (type, pointer). So you should never take a pointer to an
> interface. Just pass the interface value, and it will copy the (type,
> pointer) pair.
>
> However, when you extract a value from an interface, it *will* always copy
> the internal value. This avoids aliasing issues: someone who passes an
> interface value to someone else, won't expect the recipient to be able to
> change the sender's copy.
>
> e.g.
> https://go.dev/play/p/u5y3Kwm9Ydz
>
> Of course, if your interface *contains* a pointer, then the recipient of
> the interface can modify the thing being pointed to.
> https://go.dev/play/p/o_XAJtNuyGF
>
> But they can't modify the pointer itself held within the interface, to
> make it point to something else.
>
> The short version is: avoid pointers to interfaces, as the FAQ says.
> Instead, let a concrete pointer value satisfy an interface.
>
> On Friday, 25 November 2022 at 07:40:59 UTC Nigel Tao wrote:
>
>> Possibly relevant:
>> https://go.dev/doc/faq#pointer_to_interface
>>
>
--
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/948dc8f3-385e-4f50-a44b-ddf4792e6362n%40googlegroups.com.
Re: [go-nuts] How to cast *interface{} into *T ?
Ok, finally got it: https://go.dev/play/p/QFQOpqWsR6S
Thanks everyone, especially Axel
On Thursday, 24 November 2022 at 23:14:27 UTC Denis P wrote:
> Ok, looks like it doesn't work.
>
> I have got the following error:
> panic: interface conversion: interface {} is MyStruct, not *MyStruct
>
> So the actual code is this: https://go.dev/play/p/jBiPII7rOxG
>
> Cannot find out what is going on :-(
>
> On Thursday, 24 November 2022 at 22:29:21 UTC axel.wa...@googlemail.com
> wrote:
>
>> Hi,
>>
>>
>> On Thu, Nov 24, 2022 at 11:16 PM Denis P wrote:
>>
>>> Hi guys, tried to look everywhere and cannot find an answer.
>>>
>>> So literally I have this:
>>> ```
>>> var result interface{} = &MyStruct{}
>>>
>>> ...
>>>
>>> return result.(*MyStruct) // Error: invalid operation: result
>>> (variable of type *interface{}) is not an interface
>>> ```
>>>
>>
>> No, offense, but you literally do not have that code, because the error
>> message does not fit that code. In your code, `result` has type
>> `interface{}`, whereas in the `return` statement, according to the error
>> message, it has type `*interface{}`. Ergo, you are either shadowing
>> `result` in-between, or the code is not equivalent.
>>
>> In any case, the immediate solution could be to dereference the pointer:
>> return (*result).(*MyStruct)
>>
>>
>>>
>>> Is there any way to get the &MyStruct as a result?
>>>
>>> --
>>> 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...@googlegroups.com.
>>> To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/golang-nuts/25da3c8f-6126-439a-904a-5fec59cb09f4n%40googlegroups.com
>>>
>>> <https://groups.google.com/d/msgid/golang-nuts/25da3c8f-6126-439a-904a-5fec59cb09f4n%40googlegroups.com?utm_medium=email&utm_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/ee00cfa3-cdcb-4756-9cf6-9cfcc9abbf12n%40googlegroups.com.
Re: [go-nuts] How to cast *interface{} into *T ?
Ok, looks like it doesn't work.
I have got the following error:
panic: interface conversion: interface {} is MyStruct, not *MyStruct
So the actual code is this: https://go.dev/play/p/jBiPII7rOxG
Cannot find out what is going on :-(
On Thursday, 24 November 2022 at 22:29:21 UTC axel.wa...@googlemail.com
wrote:
> Hi,
>
>
> On Thu, Nov 24, 2022 at 11:16 PM Denis P wrote:
>
>> Hi guys, tried to look everywhere and cannot find an answer.
>>
>> So literally I have this:
>> ```
>> var result interface{} = &MyStruct{}
>>
>> ...
>>
>> return result.(*MyStruct) // Error: invalid operation: result (variable
>> of type *interface{}) is not an interface
>> ```
>>
>
> No, offense, but you literally do not have that code, because the error
> message does not fit that code. In your code, `result` has type
> `interface{}`, whereas in the `return` statement, according to the error
> message, it has type `*interface{}`. Ergo, you are either shadowing
> `result` in-between, or the code is not equivalent.
>
> In any case, the immediate solution could be to dereference the pointer:
> return (*result).(*MyStruct)
>
>
>>
>> Is there any way to get the &MyStruct as a result?
>>
>> --
>> 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...@googlegroups.com.
>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/golang-nuts/25da3c8f-6126-439a-904a-5fec59cb09f4n%40googlegroups.com
>>
>> <https://groups.google.com/d/msgid/golang-nuts/25da3c8f-6126-439a-904a-5fec59cb09f4n%40googlegroups.com?utm_medium=email&utm_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/d1a148b6-99f1-47fa-9c4a-4c8823fb15acn%40googlegroups.com.
[go-nuts] How to cast *interface{} into *T ?
Hi guys, tried to look everywhere and cannot find an answer.
So literally I have this:
```
var result interface{} = &MyStruct{}
...
return result.(*MyStruct) // Error: invalid operation: result (variable of
type *interface{}) is not an interface
```
Is there any way to get the &MyStruct as a result?
--
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/25da3c8f-6126-439a-904a-5fec59cb09f4n%40googlegroups.com.
[go-nuts] Method chaining in multiple lines
Hi guys,
I am struggling with making my code work in a way that multiple methods
called in multiline approach. Does any gopher has an answer is there any
solution to this:
```
type MyStuff struct { }
func CreateMyStuff() MyStuff {}
func (s MyStuff) DoJobOne() MyStuff {}
func (s MyStuff) DoJobTwo() MyStuff {}
...
result := CreateMyStuff()
. DoJobOne() // Error: expected statement, found '.'
. DoJobTwo()
```
I have an error " expected statement, found '.' ".
Is there any workaround?
--
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/182bae0c-de3f-417e-82bb-07ca3d26e71an%40googlegroups.com.
[go-nuts] cannot initialize 1 variables with 2 values
Hi guys,
Does anyone know how to pass it properly and without adding extra lines of
code?
```
func GetAsOr[T any](t interface{}, e error) (T, error) {
return t.(T), e
}
func (s ServiceProvider) GetServiceOr() (interface{}, error) {
}
result := GetAsOr[MyObj](services.GetServiceOr()) // Error: cannot
initialize 1 variables with 2 values
```
--
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/308dd860-a980-449d-a710-201f074e4358n%40googlegroups.com.
