To clarify - the author of the package enforces immutability. With Go’s design
this can be a simple comment on the field. The package shouldn’t be that large
where this doesn’t work.
> On Nov 21, 2019, at 10:58 AM, Robert Engels <reng...@ix.netcom.com> wrote:
>
>
> Correct, but if the receiver method is mutating it, then it is not an
> immutable object.
>
>
>
>
> -----Original Message-----
>> From: burak serdar <bser...@computer.org>
>> Sent: Nov 21, 2019 10:53 AM
>> To: Robert Engels <reng...@ix.netcom.com>
>> Cc: advanderv...@gmail.com, golang-nuts <golang-nuts@googlegroups.com>
>> Subject: Re: [go-nuts] Enforce immutability through static analysis
>>
>>> On Thu, Nov 21, 2019 at 9:49 AM Robert Engels <reng...@ix.netcom.com> wrote:
>>>
>>> They can't unless the instance field is exported. Just hide it via
>>> encapsulation with accessors.
>>
>> Can't do that with a receiver. All methods of a type are in the same
>> package as the type, so all fields are visible to the receiver.
>>
>>
>>>
>>> -----Original Message-----
>>> From: advanderv...@gmail.com
>>> Sent: Nov 21, 2019 10:15 AM
>>> To: golang-nuts
>>> Subject: [go-nuts] Enforce immutability through static analysis
>>>
>>> Dear Gophers!
>>>
>>> I was wonder if it possible to force immutability on the method receiver? I
>>> know Go doesn't support immutable types and that it is possible to pass the
>>> receiver by value but if the receiver struct has a field with a pointer
>>> type the method may still manipulate it:
>>>
>>> type Counter struct {
>>> n *int
>>> }
>>>
>>> func (c Counter) Render() string {
>>> *c.n += 1
>>> return strconv.Itoa(*c.n)
>>> }
>>>
>>> I would like to force (or hint) the the user in writing interface{ Render()
>>> string } implementations that don't manipulate the method receiver. So that
>>> they can be considered 'pure' in the functional sense of the word and can
>>> be called repeatedly without side effects. I would like the user to be able
>>> to define implementations of interface{ Render() string }such that I can
>>> safely call the method and use the returned string to write a http.Reponse
>>> without it changing between requests.
>>>
>>> I control the way in which Render is called and I am open to crazy answers
>>> such as:
>>>
>>> - Maybe it is possible to use reflect to "switch" out the value receiver
>>> for a temporary value which is discarded after every call?
>>> - Maybe i can use static code analysis to warn the user? How feasible is it
>>> to prevent all cases of this happening with just static code analysis? can
>>> this be done at runtime?
>>> - I could instead ask the user to provide a factory function that init new
>>> Counters but maybe very inefficient if the structs are very large (or have
>>> many nested structs)?
>>>
>>> Or maybe there is some possibility that I'm missing?
>>>
>>> Cheers,
>>>
>>> Ad
>>>
>>>
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>>>
>>>
>>>
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