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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