I'm sorry, but isn't the way you enforce immutability is that you don't code
mutating exported methods? The author controls the package code. Immutability
is usually only a concern outside the package, and that is clearly supported.
-----Original Message-----
>From: burak serdar <bser...@computer.org>
>Sent: Nov 21, 2019 11:34 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 10:25 AM Robert Engels <reng...@ix.netcom.com> wrote:
>>
>> I don't think we are talking about the same thing. You can certainly code an
>> immutable object - just don't export any methods that mutate the object, nor
>> export ANY fields.
>
>Correct, we're talking about different things. The question is not
>whether you can write an immutable object (yes you can), it is whether
>there is a way to enforce the immutability of the receiver of a
>method.
>
>If the method is exported and if the receiver contains pointers, there
>can be no guarantee that the method will not modify values reachable
>from the copy of the receiver.
>
>>
>>
>>
>>
>> -----Original Message-----
>> >From: burak serdar <bser...@computer.org>
>> >Sent: Nov 21, 2019 11:09 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 10:05 AM Robert Engels <reng...@ix.netcom.com>
>> >wrote:
>> >>
>> >> 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.
>> >
>> >The original problem remains: there is no way to enforce an immutable
>> >receiver.
>> >
>> >>
>> >> > 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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>> >> >
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>> >>
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