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
>
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>> .
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>
>
> --
>
>
> Thanks & Regards
> Deeptiman Pattnaik
>
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